be careful of moisture
if you can put good weather stripping on the garage door - usually these have a BIG space all around (Especially at the top where it may "bend" to follow the rack mechanism). It depends how the door is built of course but double check.
also you should consider "finishing" the walls if they are not insulated i.e. no fiberglass panels between the studs. At least put up some thick fiberglass panels; staple the sides to the studs, there is generally paper wider than the fiberglass for this purpose. This will keep the heat inside (and the cold outside).
Again if your walls are not finished, and if you want to be comfortable in there if your area is cold, put up 1 layer of 5/8" SHEETROCK. It is easy just nail to the studs every 10 or 12 inches. The mass and thickness of the sheetrock will help keeping it (a bit) quiet. It is *not* going to soundproof the place but it will be better than nothing.
I hope this helps!
-mano