Can you rule out that you're becoming deaf?
Never underestimate PEBKAC.

I don't think stable fps have ever been a thing in TF2.
That's more of a config than a build question.

No, the only things that matter so far is nVidia support FreeSync/Adaptive Sync now, but still refuses to admit it and Zen2 is looking gooooood.

What game? Also what's "lower than 1080p res"? 1079p? 900p? 720p? 480p?

Glad I could help.

I almost forgot to check but the Z390 M Gaming is compatible with the NH-D15, it shouldn't block the top PCIe slot. https://noctua.at/en/products/cpu-cooler-retail/nh-d15.html?comp=1
However that doesn't include backplates so try to avoid GPUs with ridiculously thick ornamental backplates and/or double check just to be sure it'll fit if it got a backplate at all.

CPU:
If you use hardware encoding even the 9700K would be a waste of money, the 9600K would be more than enough.
With software encoding the 9900K isn't that much better. The problem is either both get more than 144 fps or neither, it's usually not that close. If you're willing to drop the settings while streaming or don't need 144 fps in slower games or just don't stream at 1080p, 60fps, 6000 bitrate (not sure how good your connection and twitch would even be at maintaining that) then the problem dissappears for both.
Overclocking also factors into this. Even the 9900K itself overclocks higher with Hyperthreading disabled, so the overclocked you'd expect the 9700K or 9900K with HTT off (some people do that) to always win in games and close the gap when streaming.

Mobo:
It's perfectly adequate if you're not doing anything crazy.
https://www.overclock.net/forum/attachment.php?attachmentid=231464
>200W is difficult to cool and you're not using this for benchmarks, so there's no point in not using an AVX offset.
With the 9700K it's even less of a concern.

RAM:
Ranks don't factor into this.
Also more sticks are generally less stable.

GPU:
You're already into overkill territory and the higher up you go the worse the price to performance ratio gets. Stick with a reasonably priced 2070, unless you absolutely need the extra power. In those cases you go straight for the cheapest 2080, which is significantly faster instead of the most souped up 2070 that gets you 3% more fps for 50€.

Case:
Ok then.

PSU:
Overcurrent protection usually kicks in 100W above the rated wattage or even later.
Techpowerup actually tests at 110% and guess what happens?
https://www.techpowerup.com/reviews/EVGA/SuperNOVA_G2_750/5.html
https://www.techpowerup.com/reviews/EVGA/SuperNOVA_G2_750/9.html
Absolutely nothing.
They are rated to run continuously at 100% for 10 years so they could take 120% easily. The only thing stopping you from doing that is OCP kicking in as a way to tell you "if you're running this far over the rated wattage you've either miscalculated massively or something has shorted out so let's not find which one it is by waiting to see if the PC catches fire".

Cooler:
Cheaper yes, probably good enough for most things and certainly better than the first cooler you chose, but not on par with the D15.
If you draw more power the gap becomes wider.
https://www.tweaktown.com/reviews/8842/quiet-dark-rock-pro-4-cpu-cooler-review/index6.html
The D15 is not that impressive on most CPUs because it's simply overkill. For 100W a single fan single tower cooler can get you the same temps at lower noise levels if you're using fan control instead of 100% 24/7. Above 150W is where the fun begins.

http://www.coolingtechnique.com/img/rece/dissipatori/cryorig/r1-universal/stock_load.png

This shows it best. Above 150W the jumps get bigger, like they should, except for the D15. That curve somehow flattens out. At 100-150W it's somewhere in the middle of the pack between all the All-in-one watercoolers (which are way louder) and a maybe a bit below most other big air coolers, but beyond that it's suddenly 2-4°C below even the 240mm Aios and only the 280 and 360mm can compete (at 20dB more).

Maybe take a look at Le Grand Macho RT. Either way a really good single tower or decent dual tower (both ~60€) should be enough if you don't do anything crazy and only end up pushing 200W through the CPU. If you are concerned about the mobo and get the 9900K and really push it and draw >250W then something like the NH-D15 is worth the money. I put it in as the most expensive cooler that would still make sense to make the budget planning easier, should you want to upgrade anything else with the "saved" money (e..g 2070->2080 like you mentioned).

HDD:
WDs tech is so good they abandoned it completely and are now using Hitachi's tech almost exclusively. Guess why you didn't hear about Toshiba? Guess who didn't even make HDDs for years and got some of Hitachi's fabs for regulatory reasons? Yep, it's Toshiba. In other words the old WD drives are worse and the new WD drives are the same.
Either way there's also some Seagate and HGST (Hitachi brand post WD takeover) options (including prosumer and actual enterprise level drives) way below the price of the WD Black. Paying a premium for "high performance consumer HDD" doesn't make sense when any SSD is going to be much faster anyway.

AMD:
The 9900K and 9700K are already selling way above MSRP and they only compete against existing CPUs. They are not artificially underpriced because everyone expects some mythical CPU to be way better next year. There's always a better CPU next year.
The only thing that could've happend would be AMD launching better CPUs and driving the prices down, but not up.

Yes, probably both overkill but the 9700K is a fairly sane choice. AMD's next generation is still a few months away and when not streaming the 9x00K simply win based on the higher clockrate.
There shouldn't be too much of a difference between the two, what benchmarks did you look at?

Yes, µATX is fine. You could get a µATX case as well. Not something tiny where building is a pain, just a bit more compact and cheaper.

What would be the benefit of 4x4GB?

Yes, the 1080 Ti is EOL and the 2070 is about as fast and about the same price (which is kind of sad for a new generation of GPUs, to only keep the price/performance ratio). It doesn't have to be the most expensive 2070 though, an extra 100-150€ don't get you that much. At some point it makes more sense to simply buy the cheapest 2080 instead, which would easily be faster. I'd recommend sticking with a more reasonably priced 2070 though.

It might be possible to find a similar µATX case. But we'll leave that for last.

The PSU isn't bad but there's far better options at that price.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=456
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=500
https://de.pcpartpicker.com/product/sMM323/evga-supernova-g3-550w-80-gold-certified-fully-modular-atx-power-supply-220-g3-0550
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=529
It's not even close.
I went with the 550W Platinum version, but if you really think you need 650W (you don't) you can get the 650W Gold version for about the same price.
https://de.pcpartpicker.com/product/WrNypg/seasonic-focus-plus-gold-650w-80-gold-certified-fully-modular-atx-power-supply-ssr-650fx

Two more things: The cooler isn't that great, only just about keeps up with coolers half the price.
The HDD doesn't make sense, it's massively overpriced. Even if you want a 7200 rpm there's far cheaper options.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i7-9700K 3.6 GHz 8-Core Processor (€429.00 @ Caseking)
CPU Cooler: Noctua - NH-D15 82.5 CFM CPU Cooler (€87.99 @ Aquatuning)
Motherboard: Gigabyte - Z390 M GAMING Micro ATX LGA1151 Motherboard (€141.94 @ Mindfactory)
Memory: Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3200 Memory (€115.22 @ Amazon Deutschland)
Storage: Samsung - 970 Evo 250 GB M.2-2280 Solid State Drive (€72.90 @ Amazon Deutschland)
Storage: Toshiba - X300 4 TB 3.5" 7200RPM Internal Hard Drive (€105.42 @ Amazon Deutschland)
Video Card: Gigabyte - GeForce RTX 2070 8 GB WINDFORCE Video Card (€529.00 @ Caseking)
Case: Cooler Master - MasterCase H500P Mesh White ATX Mid Tower Case (€155.89 @ Alternate)
Power Supply: SeaSonic - FOCUS Plus Platinum 550 W 80+ Platinum Certified Fully-Modular ATX Power Supply (€100.99 @ Amazon Deutschland)
Total: €1738.35
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-01-06 23:57 CET+0100

More or less the same build, same performance, but 300€ cheaper.

Why would AMD hike the prices?

Honestly if anything that's an argument against buying from a Croatian shop rather than an argument for the VG248QZ. Glorious EU free trade area.

Good luck dealing with ASUS support in Eastern Europe. I stand by my prediction of a few months.

It's a firmware bug, it'll probably be fixed some day, but if you want to use 144 Hz now and not just in a few months I wouldn't recommend buying it.

Then again the VG248QE had PWM and worse colours than pretty much all other monitors, was severely out of date and overpriced and people still bought it. So the VG248QZ with no 3D support and no actual 144 Hz at an even higher price carries on the tradition of offering a monitor that's worse than even the cheapest budget 144 Hz monitors at a higher price.

Somehow I doubt that this will stop people from buying it.

Honestly just use hwmonitor, because either you're doing it wrong or the CPU is sitting at 800 MHz under load and we need to look at max clockrates anyway.

I said tomorow at 0:59 so technically I'm a day early. Underpromise and overdeliver.

First of a few things that are basically fixed:
https://tweakers.net/pricewatch/1051069/intel-core-i3-8350k-boxed.html
https://tweakers.net/pricewatch/430394/thermalright-macho-rev-punt-b.html including shipping the H7 costs ~44€ instead of the 30-35€ it should cost and it's a bit on the low end of what you'd want for a good overclock so might as well take the ugprade.
https://tweakers.net/pricewatch/1131813/samsung-860-evo-500gb.html
https://tweakers.net/pricewatch/1117319/seasonic-focus-gold-450w.html same here, hard to find anything decent that's cheaper so might as well get something much better for the same price
https://tweakers.net/pricewatch/1122045/benq-zowie-xl2411p-(met-color-vibrance)-zwart.html

I haven't looked for a case yet and it depends a bit on how the variable parts of this add up. The Q300L is still a valid choice.
https://tweakers.net/pricewatch/1150039/cooler-master-masterbox-q300l.html

Now for the mobo:
https://tweakers.net/pricewatch/1255169/gigabyte-z390-m-gaming.html works but if you go for a full ATX case and don't mind the worse onboard sound (onboard sound is always terrible and should never be used) you can get pretty much the same thing for 20€ less
https://tweakers.net/pricewatch/1252061/gigabyte-z390-ud.html

RAM:
https://tweakers.net/pricewatch/466656/g-punt-skill-ripjaws-v-f4-3200c16d-16gvkb.html
https://tweakers.net/pricewatch/1073899/team-group-vulcan-tlred416g3000hc16cdc01.html
Basically a way to save 30€ to make the budget work out if it has to at almost no performance difference.

GPU:
https://tweakers.net/pricewatch/1156001/sapphire-nitro+-radeon-rx-580-4gd5-(11265-31).html
https://tweakers.net/pricewatch/567281/zotac-geforce-gtx-1060-amp!-edition-6gb.html
A bit faster, a bit quieter, maybe overclocks a little bit better, probably worth the 20€ more if you don't mind the whole registering and logging in to get a driver and nVidia being nVidia in general.

I haven't asked when you'll actually build it, so the prices might change a bit until then, that's why I tried to stay within those 1100€. RAM can obviously be changed to whatever is cheapest with the same specs, with the GPUs you have to ignore mini-iTX/small form factor versions and generally 1 fan designs, but other than that it should stay the same.

You can now decide on the full ATX vs micro-ATX thing, whether or not to take advantage of the cheaper full ATX mobo. A larger case might cost 20€ more so all you'd end up with is a larger case but it could be cheaper and maybe there's a full ATX case you like more (or that comes with more fans).

It should, there's different 1060s and different cases so we can definitely make that happen.

Yeah, pcp nl simply doesn't know a whole lot of shops.
If you're fine even with ordering from german shops I can definitely come up with something better than the first list tomorrow.

The max is worthless if you started the program after closing TF2.

Yeah, a second fan would be the bare minimum. The case was mostly a placeholder with an approximately realistic price.

Shouldn't be that much more expensive.
https://tweakers.net/categorie/49/videokaarten/producten/#filter:q1bKL0pJLXLLTM1JUbJSKijKzCpW0oEIBucXlQDFEouT4SIFqcmeQHW6hjogpcmpvpl5SlYGOkrFQAm3zJyS1KJiJatqJSMjEFmWmKNkFa1kaGBoZKwUW1tbCwA

Look for cheaper RAM as well if you know what to look for.
If you tell me which shops you'll be using I can do it for you, especially mobo and PSU are a bit more complicated.

Ok, look for a case that you like (if it's not a good one I can still look for one that looks similar), decide how much storage capacity you'll need and I'll make the final partlist tomorrow.