Your questions shows that you are really new to android , so first I'll recommend messing with the system before installing a tablet in your car
as far as your questions
1.There was a frontend attempt ( AndCar ) , but the dev seems to stop supporting/developing it. Most launchers will provide you with enough flexibility to do whatever you want with a little bit of work..
2.Yes , using apps like Tasker
3.Depends on the OS/Device - usually quick enough
4.Not most but ALL of them.. Android is Touch-Oriented as a system
5.You need a USB OTG/Host capable device
6.external HDD ( FAT32 ) , Keyboard , Mouse - most devices with usb otg/host support them out the box
For other usb devices you need app/drivers which might be harder than you think
for example USB cameras are not supported on any device I know at the moment
Drivers must be compiled with the specific device kernel , so it isn't like installing driver on windows machine
As far as android version , there is no doubt that it's Ice-Cream-Sandwich ( ICS )
If you have any more questions or need me to elaborate on a specific subject feel free to ask..