On my 97, I didn't have to drill a hole in the firewall. It had a rubber grommet above left of the brake pedal. You can see it from the engine compartment as well. Took down the kick panel to access the area.
I recently ran 20ft of 8 gauge power wire to the battery. It was the perfect length. Don't buy those amp wiring kits. Go to Radio Shack and buy bulk wire. Also, they sell the gold connectors and fuse links for amps and such.