Product Page Uploads and Automatic Updates
You probably will have to alter the 'ubercart product-content type' and add some taxonomy fields to create the categories (electronics etc.). (Not sure if ubercart has this by default.)

Then you will have to use a view to override the ubercart product page. Look into views and Contextual filters. You can for instance create a block (user-product-block) and use a contextual filter to fill this. You can choose to get the user id from url and then select all products created by that user.

Filtering by category is exactly as done on the page above.