not much to add-- you seem to have a good game plan.
1. i highly recommend a local person for any fabrication work as long as they are good(all the shops in my area are horrible). it makes it easier for you to show them what you want. if there isn't anyone local, try pming nexson here-- he does some amazing fab work as well-- his proof is all over the fab section.
2. treat the carpc just like a normal stereo for connecting it to the amps. you should not need much more then a 3.5mm-to-rca-adapter cable.