First off, I am new to the forums and have already ordered my carpc, but I think I can help you out a little here. I want to say that you have good tastes sticking with Alpine, as is what I am using in my car. I am using two type-e 12" subs in seperate vented boxes. They sound good, but I am honestly close to getting rid of one since I don't use it to it's full potential. I would stick with 1 10" alpine (whatever model is desired) or possibly 2 10" subs if you listen to various types of music. A good friend of mine has a Honda CR-V and where a spare could fit in his trunk, he is using a JBL stealthbox designed for his car with a single 10" (Type S, I believe) and it is definately enough bass. I think a 10" would provide enough bass, but not be over powering to listen to. Sorry if I am rambling but, I hope I was able to help you a bit.
PS: Unless somebody has proof, I honestly think I have been underpowering my 2 12" subs for about 5 years and they are still holding up. I would take that warning lightly. But as LeVar Burton from Reading Rainbow says, "Don't take my word for it."