All you need to do is turn the handlebar of the bike against the wall 90 degrees so it sits flat and alternate the direction of the rest of the bikes.
turning the handlebards 90 degrees really helps to reduce the ammount of space a bike will take up. another trick i learned from bikes not bombs: remove the pedals! they often get hooked on one another, stuck in the spokes, etc. then yeah, pile 'em or hang 'em (you can get rubber-coated hooks from any hardware store - thread them into some thick ply wood (better thank 2x4s because they don't split) and mount the plywood to the ceiling or walls).
as for finding space to keep your bikes, we're just starting to sort that out. i've found that there are people with empty garages, corners of wharehouses, parking stalls, etc. if you can't afford to rent, let people know you're looking for space and you might get lucky and get some donated.
good luck!