Am I going about this the right way?

Before I start, I am not very good at explaining tekkie stuff...

I am trying to create a site like 'etsy' and 'big cartel' where people can sign up and start their own store on an overall domain.

I have attempted to have a go myself (with my limited experience), just to get the ball rolling:

http://www.buyuniqtest.info/

I've kind of bodged that first page so it goes to one of the example stores. That's about as far as I can get.

Create it so that when someone creates a 'store', it is already setup with the correct shopping widgets down the right hand side and they can change the banner at the top so there is a bit of customisation.

The site needs to be able to charge people a monthly fee for setting up a store too.

Am I missing a theme or plugin that can make all of this much easier?