Lovely map! I honestly love where this is going, and this map might be one of my favourites aesthetically! The themes you go with are very interesting, and I've always found it cool when people go for multi-stage maps that have more or less points on the next stage. If I may though, I would like to express some criticism and possible changes for the map. Please feel free to take them worth a grain of salt, but I do feel like some changes could make this map excellent for gameplay as well.
There are a few inclines/stairs (as shown below) that I feel are a bit too thin for gameplay. When trying to move around the map easily, I found myself often getting stuck or missing inclines entirely since they were quite thin. I imagine combatting players while trying to move across these kinds of inclines will prove quite difficult, and make things a little harder to manage. Some of these staircases could probably be a bit wider, or ramps could be a bit wider, though that's just my opinion. I will say that the ramps you use make trimping quite easy, so props for that!
Areas with map geometry that is very steep/vertical (shown below) in my opinion also makes for difficult terrain to fight on. The only offender I can think of in this regard is this very steep hill near B on the first stage. While it's not awful, the idea of having to fight someone as say, Soldier, on this hill, trying to hit them with rockets, seems quite difficult. Of course, this is under the assumption that this hill is supposed to be fought on at all. I took that assumption from the fact that it was right in front of the point, assuming that you would want to be a little further up in order to create a defensive line in front of the point. If it was simply meant to be a sightline blocker or an area to advance from, then I understand completely.
Honestly I take this point back! After many play-sessions on this map, I can comfortably say that the geometry is lovely the way it is. Makes for interesting sightlines and fights!
The final point of the second stage is also a bit of a worry (shown below). While it looks quite nice, I worry that the dark foliage will make spotting a sniper in the distance quite difficult, and spies will also be able to hide in the dark leaves as well quite easily. Spotting buildings like sentries and teleporters among the dark greenery also seems like it would be a bit difficult. I think a way this could be fixed would be to lighten up the colours of the greenery, or tone down on the foliage a little bit (though I think doing both would be awesome too). I feel like this would make visibility on this point a little easier, as it's a stark contrast to the rest of the map, in my opinion.
Another thing I feel an issue about is Red's last spawn (shown below). I feel like allowing enemy Blue players to enter this area and roam around could be a cause for contension, and an easy way to fix it could be to extend the spawn room a little bit, though keeping the resupply cabinet where it is of course. Although there are three doors, they're all at around the exact same spot. Allowing classes that excell at very close range combat to NOT get that close to Red's spawn would be a very nice change to see. I crappily drew on some func_respawnroomvisualizers so you can kind of see what I mean.
Speaking of those doors; my final point for contension would be them, but this is more aesthetically than a gameplay problem (shown below). My last issue mentioned was pretty much the last point I wanted to make, so feel free to ignore this one if you like the doors the way they are. Essentially though, these doors feel a little bit clunky. Having three of them right beside each other feels a little odd. While it does make it easy to immediately run for the dropdown, or the left and right doors, aesthetically it just looks a little... off. I feel like it could be fixed by making it just two wider doors, or just one big door, though of course that's just my opinion. Feel free to do anything you want! I'm mostly looking at these things from a player's perspective.
Other than those things, the map looks wonderful! I'm all for more Attack/Defend maps, and if they have multiple stages, even better! Good luck with the map, as like I said, it's very pretty. Looking off at the scenery in the distance give me Black Mesa vibes (specifically the outdoor sections), and I simply love the giant drill Blue spawn, the ruins, and the lovely inclusion of TF2's signature wacky buildings that make no sense functionally. It just feels like it belongs in TF2! Keep up the amazing work!
EDIT: As a side note, I also think it would be very cool if you added some more screenshots to your "Overview" section! I think it would be very helpful in letting people have a better grasp on what they're getting into when they download the map.