any amount of 10s is good, i perfer 10s, 12s are too low for the celica, thats my opinion, but ive had 3 in a cavalier and it is loud, with a larger number of subs 2+ you will have to do a sealed box because of size, with 1-2 you could do a ported, which sounds louder and ported properly will give you up to 3db more, which in acoustics means 2x as loud, sealed are cleaner though and give you the best sound. This is up to you, just remember with car audio and many other items, you get what you pay for, dont skimp out!! good luck, let us know what you decide!