1) Which scroll wheel?
2) You can run 2.x alongside 3.x until such time as 3.x modifies the database in a manner that 2.x can no longer read it. It is safe to uninstall 2.x, your database will remain untouched.
3) The arrow key works for me (at least on a Mac). I have the folder selected and I press the right arrow - the folder opens and I'm at the first playlist within that folder. Did you perhaps assign the right arrow to a keyboard shortcut?