Actually, the people running things here really appreciate it if you restrict your posts to one issue only, so you should actually have written 3 posts. 
I believe this is also mentioned in the FAQ which is recommend reading if you haven't done so.
As for your questions:
- I don't think you can add custom commands to the tree. Alt+LeftDblClick is tied to open in new tab by default, but that only seems to work in the lister and not in the tree.
2,3. I don't have Vista so can't help you there.
Regards,
Anakha