plugins and such

Hi,
I need some help in deciding which plugins I need to accomplish the following:

I want to create a membership site similar to wordpress.com and need to know what plugins I will need to accomplish that and set up google type ads on the site and to allow for other paid advertising on the site.

Currently my site ia a pr3 site. I also need to know how to change the html and set up a main page for the site.

Thanks.