Your alt should ground itself being bolted to your car. If you want to kill the lows, you'll want a larger enclosure for more displacement and for it to be tuned low. Tuning low will help on low end but your higher frequencies won't be as loud. I would suggest having a custom enclosure made for those subs, with your listening goals in mind. Also you definately want to have all the same wire throughout the car. Each piece is probably going to have a different strand count and then you wire is only as good as its weakest link. Also you want your grounds to be the same size as your power wire, since both complete the circuit. I run Shok 1/0 through my car and I love it. Super easy to work with and a 5250 strand count. Awesome stuff. Plus for $115 for a 50' spool its a heck of a deal. The DMM can be used to set your gains so you know when you're reaching full tilt (maximum output) at what volume. Generally you set full tilt at 75% volume on your HU. As far as if your alt is large enough, take how much RMS you plan to run and divide by 14.4. That will tell you how many amps you are pulling off your alternator when the amps are at full tilt. Of course you won't always be playing at full tilt, so any less than that will mean less current draw. The additional batteries will help to maintain voltage.