get the biggest XS power batt you can fit under the hood (i would think its a D3400)
and do the big 3 in all 1/0, that will help alot.
you could get away with that single batt and your stock alt, just get a volt meter andt keep a eye on your voltage, then upgrade the alt later on, unless you got the $$, then hell yea do both!you can never have too much power