alpine type r 12’s

Problem with a premade vented box is that the tuning freq and size is most likely not optimum for your subs.  The type r should be tuned pretty low...I would tune in the 20's...and the box size on the large side.  Finding a premade box like that, I don't know.  I'll bet the box you have your eye on is tuned to 40 Hz and gives each sub 1.25 cu ft.  About right?  I would need to look at the specific Type R model a little closer, but my bet is for 2 or 2+ cu ft per sub with box tuning at mid-20's. 

I don't like the idea of buying a premade vented box.  But, sure, it could be done if it's a good match for the subs in question.  The subs can share the same vent...they don't each have to have their own.

That's fine. Get 2Ohm woofers (if you plan on having one on each amp) to get max output from amps. Your remote wire idea seems fine. Just don't use it on more than say 3 things or it'll stop working (from having to power-up too many things). You'll need to do the Big3 Upgrade to supply enough power to the amps.

What kind of vehicle, HU, etc...?