I want to build an Etsy like store. How can I link the users with the main page?

I have a marketpress multisite and i want to the users could create their own shops. The problem is that I need to link the main pain cagetories (electronic,food,fashion...) with the user's categories, I mean, I would like that when you click in "Electronics" in the main page, would appear all the items related with this category from all users and shops,

How could I do it? Is there any option for doing this or other similar possibility?

Thank you in advance.

Alvaro