Subwoofer beginner question?

Yes but makes sure it is low Q. Since most manufacturers do not publish this then simply go large sub sealed box - since ports resonate you should advoid them as it will add volume without the transient dynamic pressure you seek. (think of a port as smearing energy over time - it takes the back wave and adds it to the front wave of the next cycle)

As Shadorne touches on, subwoofers are quite difficult to integrate into a system. If at all possible, I would buy used or get to try new ones in your system.

If a 12" sub is measuring the same frequency response in a room as a 15" sub, how would the bigger one "pressurize" the room better?

Haven't gotten to play with it but everything i have read suggests that you may have an easier time accomplishing your goals with two subs due to the flexibility in placement relative to the room

you can search here, Asylum and Google there is quite a bit