9900k is obviously better but I don't think it's worth the extra money unless you are doing some real serious Video Editing or something.

get ryzen if you want to stream and play games

Get an RTX card if you want to stream and play games, if you insist on CPU encoding, 9900k.

FYI the GTX 1660 (Ti) use the same encoder as the rest of Turing (RTX), only the 1650 doesn't because of reasons.
A GPU upgrade just for streaming might not make much sense though if you were going for a CPU upgrade in general and just want it to handle streams well. If you're using an older nVidia or AMD card you might want to test how well your current card does before considering any upgrades.

Unless you care very deeply about the tasks where the 9900K performs slightly better (e.g. TF2 without streaming) a 3900X might make more sense. Similar for 9700K vs 3800X/3700X.

Also unless you desparately need the iGPU a 9900KF is cheaper and otherwise identical.

3700x performs similarly to the 9900k and is like 3/5th the price. Not even including over all platform cost which is higher on intel.

OK, I think maybe I might need help from you guys to pick parts for me.
Budget is right round 2000-2500 USD
I'll be playing tf2(I also use fps configs) @1080p 144hz and looking for those constant 300fps, I'll often stream tf2 as well. other than playing tf2 I'll play some ray tracing minecraft, photo/video editing, some normal stuff that a university student would need to do on his computer and maybe some code writing/programming
I'll pick the peripherals by myself, just need help on the computer. The case I'm planning on is Corsair 450D or maybe Phanteks enthoo pro m tempered glass, both are mid tower and have nice airflow but you guys can recommend me some cases too, preferably mid tower with nice airflow and good cable routing for neat cable management.

Well editing will benefit from the extra cores and you can afford it -> 3900X.
I might make a build later. If I don't just post in the pc build thread.

ryzen 7 2700x/3700x + radeon 5700 xt (better than 1080), 32gb ram (overkill but u can use it as vram in some games) 700+w psu. not including a case/cooling you’re looking at around $1100.

ryzen 2/3 is much better for streaming and playing at the same time. 16 gigs ram is plenty if you don't want to use virtualization to seperate your gaming and your streaming VM's.

750 watt should be fine

im not sure of any gpus

Get the best RTX gpu your budget allows

rtx cards are not going to net you the better performance per dollar than your cpu.
1660 ti is probably just fine for streaming tf2 and playing at the same time, as Setsul said

if all you're playing is tf2, dont go full out on your rtx cards, if you could buy a 1080ti or a 1070 you should be fine if you want to live without your RealTime Ray Tracing(TM).

rtx cards are not worth the performance per dollar

look up gpu benchmarks between 1080 and radeon 5700 xt, its $100 cheaper and performs like 15-25% better

remember not to skimp on cooling, ur shit gonna get really hot and thermal throttle if u dont cool properly

best cpu for gaming/streaming is the ryzen 7 3700x

get watercooling :)

use nvenc on a 1660ti

Ok, some more questions.
-Overclocking yes/no?
-completely new builds or will you be reusing HDDs/SSDs/whatever?
-do you want to spend 2-2.5k no matter or do you have a specific performance goal for minecraft/editing as well?

yes
completely new
*i will be using 1080p 144hz 1ms monitor
minecraft raytracing; idk what avg frames you would get so id say as smooth as possible?
editing; never done before but will try making my own frag vids and i'm pretty sure i'll have to do some educational-purpose video editing since i'll study in university next year.

'lld build this pc next march-may, ik there will be alot of new hardwares released but i just want to have a guideline of what my build should roughly looks like.
also i'll pick 1tb corsair m.2 because it's as fast as samsung's m.2 with much lower price and i'll get a 2tb hdd i think.
for the case i'll pick phanteks enthoo pro(full tower for upgrading later/easy to managing stuffs inside, good airflow, good cable routings) but if there're cases that are better at about the same price then feel free to recommend me one.

Yeah, by that time there will be new CPUs, new GPUs, new chipsets so nothing of the rough guideline would remain.
Not sure which Samsung 1TB M.2 SSD and which Corair 1TB M.2 SSD you mean because there's like 5 each.

samsung 970 evo and corsair mp510 @setsul

There's so many similar performing SSDs that I wouldn't limit it to picking between those two.
Also Phison E16/E18 and 128 Layer NAND are coming, so even if you stick with the same performance and don't go for a PCIe 4.0 SSD the prices will change a lot, even relative to each other, depending on who replaces their models first and how much the prices of the old models are cut. Choosing to buy an MP510 in May 2020 because it was cheaper than just one of its competitors in September 2019 makes no sense.