1) As you realize it yourself, it's already available (Display - Display contacts in hybrid mode).
2) Also available, it depends on the Display mode you chose for your Contact List :
- By status : They're grouped by status, so you can close "Offline group"
- By groups : They're grouped with the groups you defined, so the offline people are display.
- Hybrid : They're first grouped by your groups, then by status with an "offline group" you can close.
3) Depends on tastes of everyone, on the version of aMSN you're using (0.96 or SVN), and on the skin...
If you want no space between contacts, use latest SVN and Default skin