murk , it is the first map ever , i am still learning ... also about intersecting brushes... i dunno what the problem is :-s if it is necesarry , i will do it even if the compile time is longer.
My post chopped up into more readable, helpful sections.
1: Look at a displacement brush. Any. Select it and see it has 6 sides. Which is bad. What you need to do is select only the visible faces and create the displacements. To fix it later, select the brush, go to displacement tool, HOLD CTRL AND DESELECT VISIBLE FACES then click Destroy. That will destroy the invisible displacement faces, making them invisible. Even more. Also if you're gonna have 6 side displacements everywhere you'll have trouble sewing them. Not to mention the humongous map file size.
2: There can be only one light_environment. Well, you can have more, but having more than one is completely redundant and just calls for compiling trouble and a lights.rad syndicate strike. Or something.
3: Cubemaps should be placed in approximate middle of the room. Or exact. In bigger rooms, you have to use more than one. Or rather said, it's just what I say. Where the cubemaps are placed, the engine will take screenshots in all 6 directions, making textures that would fit precisely to texture and inside of a box with no visible lines - that's kinda how the 2D sky (the texture background) works.
4: Brushes intersecting is generally a bad thing. There SHOULDN'T be any problem while compiling, but it looks terrible since 2 different faces fight for being visible, creating a smudge on the map, marking a mistake forever. I've even seen that is some valve maps, though it's mainly models intersecting brushes (which is not a very huge problem - but again, it looks bad.)
5: Areaportals are something you shouldn't bother about yet because it will take some time to get used to the basic universal rules of not screwing up badly like everyone did in the start. In short: Areaportals are used in the engine to set what areas are visible from other areas. For example, if you have a U shaped hallway, on the top pieces only 2 areas will be visible while you're in one of the areas, but if you're in the bottom area, all 3 can be visible while being in that area.
6: Focus on the basic shape of the map for now. Don't use displacements, don't go too much into detail. Putting weeks of work into something that turns out to not be fun at all is a waste of time. Make a draft, playtest, improve, playtest, make nicer, improve, playtest, final version, final playtest, the final countdown, final version release.
7: Use JPG or PNG for pictures. Using BMP on the internet is like being on the wrong side of the stadium all dressed up at a Manchester-Chelsea game. In other words, it's a bad idea.
Well that took some time to write