I have an unlicensed copy of Minecraft and I want to buy the licensed copy?

I've made alot of stuff so far and I want to know whether or not I'll be able to play those levels with the licensed copy. Also, I've downloaded a few mods (not all of them have worked, but some still do) and I was wondering if I'd have to reinstall those mods after buying the official copy of Minecraft. I have no trouble with dishing out the $20, as long as I know I'm not going to have to deal with the hassle of reinstalling and recreating things.