First off.. I'd stick with 10's.. particularly if you listen to a wide range of music.. since the amp doesn't have the greatest dampening (control of sub), it will be easier on the amp to control a 10" vs a 12".. and in my honest opinion, 12 subs sometimes isn't enough for some people.. the truth is: YOU WILL ALWAYS WANT MORE BASS NO MATTER HOW MUCH YOU ALREADY HAVE. Its like a drug, but a good one, so I would run 2 to begin with.
If you are running 2 subs, they should be dual 2ohm to get a 2ohm load on your mono amp.
The dual 2ohm will be harder to wire up in a series parallel configuration.. the dual 8ohm subs will need to be run straight parallel.
Wiring specifics can be found at:
http://www.crutchfield.com/S-XHOzQoYmJUY/learningcenter/car/subwoofers_wiring.html