Yep, you've got it all correct. Good catch on the username limit—I think it's something extreme like 255 characters. Profile pages are associated with users by using ID numbers (it's a special field on the user account); right now they only update their titles (to match your name) when you edit them.

I'm surprised the front page is actually inconsistent in which it uses though—will need to work on that.

Also still working on the post rank stuff.