Well Damien, it sounds like you need to do some research. All of the questions you are asking have been covered many times over.
-There are all shapes and sizes of car PCs, some are very small.
-It is possible to setup your carpc so that it doesn't startup every time
-There are flip-down monitors
-Netbooks are just small laptops, you'll need to do more research to see if they will work for you
It sounds like you have a long way to go, search, search, search