1) Yes.
2) You can view 2005 database under 2008 management studio, not sure about hosting them under a 2008 instance though. I'm fairly confident they do, but not sure if it's native or via converting to a 2008 database.
3) Yes.
Note that you can't have 2005 MS and 2008 MS (management studio) installed on the same OS. This was based on my experience a long while ago when 2008 first came out, I got an error message stating that I couldn't install it because of a previous version (2005) being installed, or something akin to that. Turns out it has changed.