[Part 1]
Rehashing all the spots we went over a bit ago:
To start off, I'd recommend completely getting rid of this upper spawn door, plus the extra high ground around the point.
http://i.imgur.com/iR3mOCm.jpg
The third spawn door will make it pretty annoying balancing out both of the spawn doors in the future for your map, plus it gives easy high ground to the defending team coming out of spawn, making it the only viable exit. Try walling off that area, since it already provides some nice separation between the doors that discourages spawn camping and you'd want to keep that. The doors are also well balanced out already and have similar advantages towards agressing the point.
http://i.imgur.com/DWsxmcc.jpg
This area between the spawns is close to being alright. It gives maneuverability to the players, but promotes demos camping between the two doors, right now. To force a demo to only one door, I'd recommend either bringing the wall in more to support spam against him, or lowering the ground so that he'd be at a disadvantage, or a mixture of the two.
http://i.imgur.com/Pkp2izF.jpg
When we were talking, you said that you wanted the middle route to be the main route/choke. To promote that idea you should try creating some nice holding ground, and a way up to it. This should help teams flow into this last point, too.
http://i.imgur.com/epbfREk.jpg
Due to how this route is set up, it seems like the most viable option for it would probably be an alternate route. With that in mid, lowering this to the ground and getting rid of the bridge to the point from here will make it so that it's not overly powerful, and will give a few more options to both teams.
http://i.imgur.com/JTloR4D.jpg
With the other two routes established, this last one seems most viable as a flank. Moving this route's entrance into last up a bit will create a nice no-man's-land in between the entrance and the high ground opposite to it. Moving the holding position forward a bit, or creating high ground closer to the entrance will also help that ideal. You should also try making some kind of route around the holding position of the defenders, or towards the point (so it can be used for some flank options).
http://i.imgur.com/aiDTLEK.jpg
Currently the choke has some high ground over the flank route that separates the players coming from choke, and also gives a free visual towards the players in flank, at the same time. If you wall that off, it'll decrease vision and also focus the players coming through the choke a lot more.
http://i.imgur.com/3FBjDUl.jpg
This health and ammo doesn't make too much sense here. It promotes players holding around this position, even though they're at a disadvantage. It also isn't very likely that the defenders will rotate to here from the better positions they'll have on high ground. Health and ammo on lasts isn't really a necessity, due to the resupply cabinets, but they can support holding closer to a choke. If you found a spot that was closer to the high ground for the flank to put these, it'd probably work out a lot better.
http://i.imgur.com/f1nLEv2.jpg
A good, major change to this area would be to heighten all of the ground to be leveled. This helps with making future changes to the entrance into last, and the entrance into this lobby.
http://i.imgur.com/ZiBQnLG.jpg
Moving the wall you have set up closer to the flank entrance should make peaking into this last a bit more interesting and will open up lobby a bit more. Then you should be able to conjoin the two ramps together into one, larger ramp. This will also create a 90 degree turn in this choke, which should help with any future sight lines that might pop up.
http://i.imgur.com/x8PFqTj.jpg
Walling this off should get rid of the sigh tline you were worried about in lobby, and should help make a nice bit of separation in it, overall.
http://i.imgur.com/KYQcHFM.jpg
Adding to that, moving the general height of this down to meet up with the height on last, or making some kind of ramp up to it, should give you a few more options when it comes to changing things in the future, and also creates a no-man's-land in between this pathway, the choke, and the holding position on last.
http://i.imgur.com/SkZ5oZR.jpg
Right now this entrance is on low ground and seems very out of the way compared to all the other entrances. If you were to remove the shutter, lower the ground to meet with the other changes, and make a ramp going up to this high ground on this side of the crates, it should help increase the viability of taking this route.
http://i.imgur.com/trKsDrQ.jpg
Creating a ramp up to this high ground gives some more route options into lobby and should also help make a pseudo-holding position for flank.
http://i.imgur.com/pkc7T3f.jpg
Right now, with you wanting this to be the choke, the high ground on these crates is a bit too hard to aggress. Changing the direction of the ramp to go down to the lower creates, and removing the high ground and the crate closest to the choke should help players flowing into second. It also gives another route option up to the point that forces you to go through the defending team.
http://i.imgur.com/BEpka92.jpg
Adding to that, if you were to increase the high ground around mid and coming from the choke to be similar to the high ground given on the creates, you could create a simple, small no-man's-land in between those two spots, as well as evening out the ground between the two teams.
http://i.imgur.com/6YBkEJJ.jpg
Moving this crate and ramp back a bit should help with player movement onto the point and around this area.
http://i.imgur.com/3XZvW56.jpg
With the newly created ramp up to the higher crate, you wouldn't need these barrel crates here anymore, so you could remove them to reduce clutter. It might also help with teams coming out of the forward spawn, not having to move around as many objects.
http://i.imgur.com/xAV5aGo.jpg
This opening gives a sight line to the flank for people holding close to choke. I'd recommend walling it off to separate the two routes more.
http://i.imgur.com/QPaolnO.jpg
Right now both the flank route, and this alternate route lead to the point. If a player were to take this alternate route towards the point, people holding flank and main wouldn't be able to see them until they got to the point. I'd recommend removing this entrance and changing some of the opportunities it gives the attacking team. Also giving a visual to either flank or main if anyone is aggressing from the alternate route should help the defending team with fighting against it, as well as giving them some more reaction time (if you plan on putting a window, make sure it doesn't have immediate high ground over wherever the main holding position is).
http://i.imgur.com/zlYtnAk.jpg
Walling this off separates the alternate route from choke a bit more, and should help with some future changes.
http://i.imgur.com/9RKivjA.jpg
Right now, this choke is very open and doesn't have any direct routes leading into it from mid. Which also has the drawback of creating some pretty bad sight lines.
http://i.imgur.com/d2FodWq.jpg
http://i.imgur.com/6t0zSmf.jpg
To fix that, creating a wall with an entrance closest to the camera, added with the other wall I above, should force players to come from one direction into the choke. This'll also remove any harsh sight lines coming into mid, since it closes off both entrances on both sides of the mid.
http://i.imgur.com/fsaeK8R.jpg