I have a 2015 TC and have a Yaesu radio in it. Sounds like you just need to take your time and remove the headliner and run the cables for the antenna.
Your choice of a 4 guage power supply wire will work great just dont put too large of a fuse on it. Also, putting a fuse on the ground wire is never necessary. Just make sure the positive wire is fused.
I have searched for the service manual for my model. All I have found so far is a dvd on Ebay for around $300 that covers the TC.