most of those questions would probably get alot more help in the Fabrication section of the forum.
1. For the navigtion, just put the monitor in where your stock navigation went so that you can put it back later if you need / want to sell the car. Using the stock screen for PC use or wont work good and I dont think you can use the navi with out the head unit.
2. I doubt that there is a specific tutorial for your specific car that rarely ever happens.