Most will relocate the battery to the rear passenger side.
As for the wire size, the bigger the better! I used 2 gauge which I had lying around from a battery relocation kit I bought from Summit years ago. Most will say no smaller than "0" gauge.
I routed mine through the interior only because I installed the MAD Electrical solenoid. The cable is only hot during cranking.
Up the channel and through the passenger side toe kick area.
I used the rubber grommets through the floor. Others have used studs when going through the floor.
Being a unibody car, I grounded the battery to the body. Having subframe connectors I could have done it to the frame also. I will have grounding straps engine to frame, frame to body, engine to body. Do not overlook the importance of proper grounding!
Most of all have fun! lol
