Every amp is different. But It's pretty much guaranteed you will have over 2500 watts. Each amp should come with a birth sheet telling you want that particular amp can do. And You are correct about the ohm loads and voice coils part.
Honestly, I'd say just get a batt and possibly upgrade your front one too. And the big 3 is a must. Just watch your voltage and if it gets really low even with the batts, an alternator might be needed.
I dont know much about enclosures so I can't give any advice there.