Im currently working on a project to make an Android tablet much more car friendly and easy. So here is what I can say about your questions:
1. Not sure on this one and doing some research into so will get back to you on that
2. If you mean use your phone as a mobile hotspot then yes this is possible depending on your phone carrier, all tablets have wifi capability so this is relativily easy to set it up to auto connect when in range.
3. there are some apps out there that allow you to do automation with certain events like being plugged in or hitting a certain time, I havent gone into too much depth with these apps but I have seen them, I quick google search and you should be able to find something. To make it work you would add an event to shut it down when power it is unplugged (aka the car dock/charger isnt getting power) turning it back on though would be a little more difficult since the app isnt running
4. this is kinda a mute point depending on the tablet but I have yet to see an android device that doesnt have built in gps (and the android software comes with a turn by turn navigation built in) the only downside to this is you need some kind of internet connection to load the maps for the navigation (though getting lat/lon and general data from GPS is still capabale without it)
5. Yes!!! as this is the main focus of my current project (see my thread about an Android frontend in the forum) I am currently making an app which simplifies and makes using the android device much more car friendly.