HotLavaDestiny

Hey guys. I'm in the process of my first fairly high powered audio build (3400RMS) and need some advice on running my 1/0 cable. I have an Optima Yellow Top Group 34/78 for under the hood and a Die Hard Platinum marine Group 31 for the rear. Big 3 is complete and 220 amp alt is on the way.
My questions are....first, can both positive and negative runs be done side by side? Or do they need to be on separate sides of the vehicle?
Secondly, where the heck can I fit 2 of these things through the firewall and through the vehicle? Or do you run beneath the vehicle?
I'm finding out just how little space there is to work with in this thing the further I get. Thanks in advance for any input....I really need some advice from someone who knows the vehicle.