Url Redirection Site .overall Design Problem

Hi everyone.

I've got a rather large problem!
I'd like to create a simple URL Redirection site, where users can create urls like:
cool.as/MYNAME
(using php + mysql) but I really don't know the best way to go about it! I want to host it on a normal server i.e. hostrocket or something at first, and if it goes well, buy a dedicated server.

in the system, I would like to create features like:

allow users to check all domains for a certain extension - i.e. search all domains for myname. Then it returns all domains that do not already have folders there: like cool.as/myname, gorgeous.as/myname etc.

allow users to login, and modify their details. ie. URL to redirect to, whether or not to cloak the url, what type of banner they want, passwords etc.

allow user to modify the category their site fits into etc etc.

Now, this is all very well, but the main problem I am having about the general structure of how I would do it.
There are a few problems:
Firstly, how do I manage all the domains in one hosting account?
Secondly, how do I go about creating the redirection? Do I create an index.php file inside each folder which is made, or is there another way of doing it. And then, if the solution is to craete a file, do I create a php file which queries the database, or do I create a flat html file, which is opened and edited when a user edits their URL.

Basically, I'd like the overview solution to creating a URL Redirection site (basically the exact structure like v3.com) in PHP and MySQL.
I just need to know the structure of how I would do it. I can program it myself.

Thanks alot for your help.
-AJ