1. yes
2. no, but you've got the advantage on linux of being able to run apps with users with low access rights (I think Windows UAT copied this approach?).
3. Yes, mostly.
4. Be sure what you install is safe first. If 'viri' start appearing for the N900 then you can sure that anti virus software won't be far behind.
5. As safe as you not loosing it or installing any dodgy programs.
6. Not at the moment but I'm sure 'they'll be an app for that'