I think 2 12s. would be fine, 2 10s' could be an option, from what i have found people get one sub and wish they had more.
you need to power your mids and tweets with at least half as much amp power as the subs.
bass is pretty much equal as far as the signal goes unless u have bass cd's or bass heavy music so u have two mids and two tweets and rear fill, i have two 10s' a pair of 61/2 4 and tweets for the front and a pair of 61/2 for rear fill. My sub amp is turned all the way down with the 3 way amps set accordingly with no bass boosts up, with one sub u may find u want to turn up the bass controls.
with a pair of subs it should play music as the signal tells it to as long as everything is tuned right it should sound strong and natural but bass cab be inefficient to reproduce so most double the amp power with two subs so u never lack in the bass region.
a pair of 10's will get low enough but the 12's would be better just give the mids-n-tweets the power they deserve.