1. I don't understand, if your logged in the Welcome Panel will display the avatar the user is using. (This is if you are using the hack)
2. You can just change the image it links to in postbit_online and postbit_offline
3. It's available at vBulletin.org. The one by FireFly (Like here) is very popular.
For category backgrounds, use this mod:
http://www.vbulletintemplates.com/mo...light=category