You can set your own usertitle at 500 posts, but it can't be an image until you get to 1337.
Userbar?....I'm assuming you're talking about the pictures by "Member Level"....yeah, 1337.
Avatars go with your member level, I don't know the exact sizes, but you can get a bigger avatar for each level.
1 post = Level 1.
2,500 posts = Level 2
5,000 posts = Level 3
10,000 posts = Level 4
Or, you can donate and remove the limit from everything.