Need a guide to make the site look like a portal of multisites

Hi,

Can you help me setup to make my website look like a paid multisite portal/marketplace ?

I am referring to those "get a site, login, sign up for a site" widgets, clicking on signup would send them to a pricing table where the user can register and pay by paypal.

Then there would also be a listing/sections/widgets of all the registered sites to make it like a directory or marketplace..

I am sure its the foundation of multisite but I am overwhelmed with all the plugins, themes and features but yet this project has to take of asap.

A detail step by step would be great.