Paul,
In answer to your first question, you would have to fit the brake kit and then measure the distance needed to clear the calipers. However, spacers are nasty (unless using the proper Eibach type available from Chris @ Carnoisseur AKA Cossymad), as the wheels don't sit on the hub locating ring and can vibrate like a bastard.

In answer to your second question, 2wd discs and 4x4 discs have a different offset - i.e. when fitted to the hub, the disc sits in a different place (like you get different offset wheels).

Hope this helps....