center bore matters in that you can't fit a wheel with a SMALLER bore onto your car if it is smaller than the hub. for your example, you can get centering rings to fill in that spacing, though some will say they are not necessary. up to you.
in a broad sense...higher offset=wheel more inset in wheel well, lower offset=wheel will stick out more. to be more specific, the offset is the distance measured from the center of the wheel. use the wheel directory/gallery to see what fitment works for your own goals here:
http://www.ft86club.com/forums/showthread.php?t=7535
here's a photo to help you picture it:
