Maybe you should change the db structure, to optimize sql queries, use a caching system to delivery static content, or you can ask a more experienced developer to look over db structure and give you ideas. 9000 users don't seem that many to make the server run slow...
A scripting language (PHP,ASP,Python,etc), sql, html, js, css.
And the best way to start learning is to start doing projects, smaller at first, then bigger and bigger. You can try doing some project with something that you need.