You'll be fine with 2 or 4 Gauge cable.
I bought a "yellow top" Optima battery. It's sealed and you can locate it in your car.
Also it's deep cycle so it stays happy even when getting pounded by my stereo with the car off. (also it's nice an close to the amps in the trunk - which have their own 4 Guage)
Make sure you don't go overboard with the cable think of why you're doing the relocation in the first place (hopefully the balancing of weight) When you go adding 30+ lbs of cable it kinda defeats the purpose.
4 Guage (if you're not drawing crazy stereo power near the front) ground it in the rear and a sealed optima battery is a nice touch.
-Simon (with $0.98 in his pocket)