1. Read help included in 3dgs once again about doors

You have to use trace function, when you are close to door and looking at it or press the button they will open.
2. of'course you can. just create 10.000 polygon model (f.e. in 3dsMax, use multiple skins, alpha channels, shaders, camera effects, maybe couple of your own dll files...
3dgs supported DirectX effect so you can do everything you want to
