Starting over

Hi folks,

I'm trying to wrap my head around a few things. I had a WPMU setup several months ago but never really developed it further. I'm just now trying to get it going again and WP 3.0 came out and now I'm confused all over again.

Since I didn't have anything on my MU setup, I wiped it and started fresh with a brand new WP 3.0 install and have successfully setup the "Network" of sites. However I'm trying to figure out what to do next. My goal for my website is to allow users to set up their own websites/blogs from my main site, and charge them for premium themes and plugins.

I guess the first question would be where do the different plugins go? Has it changed from WPMU? Is there a difference for the main site plugins, the user site plugins, and the "premium" plugins that I wish to only be available to paid users? This goes for themes as well. Do they all go in the regular themes folder?

I'm very experienced with regular WP installs but the whole MU/MultiSite this is messing me up. Thanks for the help!