I don't want to discount the CarPC completely - I'm a nerd like many of us here and would love the full PC functionality and customisability.
Having said that, my thoughts were to retain the factory Nav/TV screen, hence why it would need to be remote controlled, as it's not touch screen, and to make the install as painless as possible (in such a complex car).
If I can't arrange what I want, CarPC may be the next best solution.