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Keep in mind that trade servers will often have 32 slot capacity. Fill your map with 32 players and chaos will be brought to the server. That's being said if 32 players were fighting, so let's half that, but even then, it's a bit snug.
I get that you were going for a map that was set on a rainy dark day, but in the buildings, I really can't see anything. Join a valve map, either a rainy setting or even a nighttime setting, and you'll see how brightly lit they really are and what you should shoot for when it comes to lighting in any environment.
Finally, there's the "walls that just expose the fact you're in a killbox". Basically it's my way of saying "I can see though the map in some spots." First spot is here, second spot is this, and finally there are these. I guess maybe these were design choices if you wanted, but it just feels wrong personally. It's also because of this that your map is unoptimized, and makes optimisation borderline impossible. Here's what your map looks like to your computer. As you can see, everything is rendered at once. Now it isn't much of a problem nowadays, but it's still something you want to keep on top, because as you continue to add more and more, people's computers and frames will get slower and slower.
Now for the positives about this map though, the textures, skybox, and lighting in most places all feel right. It does indeed feel like rain could appear at any second (ignoring the fact you have a palm tree near the wooden structure in the centre for whatever reason). If you wanted to build on this map, you could add ambient sounds and soundscapes. I get that this is your first map and so this stuff may be a bit too advanced, but I've been through the same stage, so if you keep at it, you'll be able to make this a brilliant map! One thing to keep in mind, if you don't want to start from scratch when making a map, don't be afraid to tear down something large. Because you've built it once, you should be able to rebuild it better AND quicker and before. I'm not saying you should do this to any specific part of the map, but since the structures are so large and you said this map took you a long time, it's something you should always consider if you don't like the look or feel of something.
If you get stuck with anything in hammer, you can add me on steam if you feel like it. I have nothing better to do nowadays and so I'll be happy to help. There are also some other TF2 mapping groups out there, like TF2maps for example. Depends what your needs are. Anyway, nice job!