When I installed an amp when I had the stock deck, I tapped the remote wire to an open spot in the fuse panel underneath the dash. The fuse was an accessory fuse and only turned on when the key was in the "ACC" position. Unfortunately, this turned on the amp whenever the key was in this position regardless if the stereo is on or not.

As for the running the power line, I ran the power wire from the battery through the firewall on the passenger side of the vehicle.



The wire will come out underneath the front passenger carpet like so



IMO, the best place to tap off the deck would be from the rear speakers. They are easier to access.