Not new to car audio, but new to higher end systems.. couple of Q's

[skittlesRgood]

At 12 volts running full tilt you will need just over 200A just for the 2.5k RMS amp. So yes, you will need a HO alternator if you plan to run full tilt with the alternator. If you plan on only using it for demos, and charge your batteries in between runs, you could get away with the stock alternator, and a bank of batteries. You will need to run multiple runs from the front to the back of the vehicle as well. Honestly it would be cheaper to get the HO Alternator, an AGM battery (XS Power is what I would recommend) for the front, and a big AGM battery for the rear. I would also run at least two 1/0 runs from the front to the rear.

your math is a little off there chief. 2500w amp at %70 efficiency and 12v brings you to 297amps. at 14v you need 255amps. so a 270amp alt and a good starting battery could be all you need. if you stick with your stock alt, you probably need a total of 220AH. so however many batteries you need to equal that.

[HelloMyNameIs]

I'm running 2.5k rms daily on one xs3100 - having voltage drop but not major and I'm thinking my big 3 I'm doing in a few weeks will end that period so you may need a few xs batts but not nessicarly a ho alt (just my experience)