1. Definitely not necessary. Besides, there's still no jailbreak for the iPad2 as of this writing
2. Just browse the iTunes AppStore. Download the free stuff that gets your attention so you can get started. You'll know what you'll need when you see it.
3. To some extent, yes. But you'll need a 3rd party app. I use Docs-to-Go. But it's very limited compared to its respective counterpart apps native in Windows. Good for editing and proof-reading docs on-the-go. But to write a 50-page doc on the iPad? Maybe not too enticing, still, it is possible if you're on a bind
4. Yes, but if used as a car nav, it'll be cumbersome as the iPad1/2 is relatively too big for the dashboard. It's ok if you use it occasionally. But for daily use, get a dedicated GPS. As mentioned above, use it as reference only, as it may not provide turn-by-turn directions.