I have the avenger and it is awesome as long as you know what ur doing and once u get over like 200lbs in the trunk the ride becomes a little tougher but that's inevitable. And you have a bigger trunk and it doesn't affect the mpg that much.
I would go with the alternator first. And i have a Singer Alternator they are a lil cheaper and just as good ou might wanna look them up and get a quote. Good luck though Dc power is a very good brand though.
Good stuff I have the same system basically and it works for what it is. It's nice having ppl think u have like 3 thousand watts and ur barely doin 1500 rms