Adding a sort function to the author list

I’m converting this site to WordPress, having already imported the list of users into wp_users, etc.

Now I’ve created a custom page template to display the list exactly like that, but unfortunately I can’t figure out how to create the sort & pagination.

Here’s the code I’ve come up with so far:
http://pastebin.com/3Fe7d97e

It displays the first 50 users, but neither the sort nor the pagination works – currently it shows the users listed by ID, not as desired by the latest registration date. I’m somewhat inexperienced with such advanced hacks, so I’d be grateful for any help.