1. For the most part, yes. I don't know about the wifi drivers, but I believe all hardware drivers for the N900 are community-written.
2. Yes right now, although the N950 is a developer device.
3. No idea (don't have one.)
4. Nokia would certainly hope so. As it stands, Meego uses a RPM based package management system, so I suppose perhaps you could use the ARM repos for Fedora or something.