A few misc comments starting at the top..
1) "Opus 90w PSU"
You sure 90w Opus will be enough?
2) "In Dash flip out monitor, the XENARC im thinking, but do they have a motorised monitor? Much cooler than having to push the thing in and out"
Xenarc has an in-dash motorized unit (700IDT - the 700 TS and TSV are the non in-dash ones) - it has some issues and was recenlty pulled from the mp3car store but you can find them elsewhere. Search for more info.
3) "which front end integrates the most effectively with which GPS application"
I like Road Runner and iGuidance.. Any frontend and gps should work fine together, that's the point of most of them.
4) "If I want to run a keyboard, a bluetooth dongle, a wireless dongle, and the touchscreen interface through the usb hub, am i likely to need a powered hub?"
You might, depends on the hardware.. some of my keyboards require power, some don't. Plug it in and try it. Most hubs take 5V, and the easiest way is to run a regulated 5V from your comp's PSU. Run a search on this.