Limit Widgets and Plugins to bloggers WPMU

Noob question here.

I noticed that alot of my plugs and widgets are freely available to the bloggers on my site (I only have 3 created test suscribers to see what they could see on the dashboard). The site is a dot (us) called “Doylestown (DOT)us”. What is the best way to limit plugins to the people that sign up for my blog. I would just like to give them a few basic widgits to blog (nothing fancy). Also I would like the users of the blogs just to have 1 basic theme, unless there is a way to have like 3-5 basic themes to use.