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It's really the tiniest details but it does make your map look so extremely much better without any of these tiny errors
Oh, Portal 2 mapping conventions. By the way, good job Lpfreaky!
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The project is going slowly, but I work on it everyday! The main problem now is the compile time (is taking like 30 minutes to compile this map), and this makes it very very hard to fix bugs 
Have you considered:
1 skyboxes: in screenshot 2 it looks like you'll never get there, if you build it in a skybox it should load and compile faster.
2 cordons: they provide much faster compile for small sections of your level.
3 Fast compiles: no need for normal or full compiles until your final compile OR when you want to test out lighting.
Also, make sure you are making brushes that dont block sight completely, func_detail.
That helps ALOT with compile times.
Take a look here: http://www.optimization.interlopers.net/index.php?chapter=intro
I think my biggest problem is the skybox thing, but how can I create a huge area, like a forest, without making a huge skybox all arround it?
The idea of the skybox is that it can be much smaller, since it will show up larger than it really is. also since you can't reach it you can use no collision model and everything in there that isn't the box itself can be func_details 
Ever heard of a 3D skybox? 
Yes, but I actually never tried it, as I don't think it will ever work (my models would have to be much much smaller, and I only have them on normal size, because there are trees all arround the outside area...)
The good thing about 3d skyboxes is you don't need to scale them down to a miniature size. You can have it as a scale as 1:1, however that really removes the point in it in the first place.
There's a tutorial on interlopers, on using Cannonfodder's MDL Decompiler to change the size of your models, which could be done for use in the skybox.
http://www.interlopers.net/tutorials/2509
The command was, after the modelname in the .qc file, to type $scale 0.0625 to convert normal models to skybox size, and $scale 16 to convert from skybox size to normal size.
Hope this helps!
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It does help indeed, but It's a lot of work, and my only map with skybox is almost done, so I think i'll just tolerate this insanely long compile time...