i can help with the second part.

get a typical amp kit then look on your amp and see if it has a built in high level in, if it does, steal the signal from your rear speakers and use that, if they dont, buy a LOC and do the same for the signal.

For routing the power wire theres a grommet in the firewall near the top of the carpet in the front passenger footwell.

Cant help with the specifics of getting to it since i dont own a 7th gen.