1) Do models stand (by that I mean that they don't fall through) on clip brushes? Yes? OK.
2) How exactly is the ingame model size defined? I mean, the space that the model occupies ingame is not the same shape as the model itself, it's a cuboid (or whatever it's called).
For example while the player model is a human, the space the player occupies is a 73x33x33 cuboid, I think (or 37x33x33 if you crouch), even though the model itself isn't 33 units wide.
So what about if I make a chair or a helicopter or a key, how large will the space that it occupies be?
3) How do I make and more importantly compile an animated model? (I have Milkshape and 3dsmax)