How do I set up a filtered search for global product categories in a multisite?

Hi there,

I’m setting up an Etsy-style multisite network with Market Press. I’ve got about 100 product categories which, using this tutorial ( I have jimmied to be global for the whole network. I already have a multi-site search widget which works great, so what I’m looking to do now is set up a filtered search which allows users to select multiple product categories (set up in separate drop boxes) to filter items returned by the search. We’re building a site to sell artworks so the criteria are to do with size, materials, price, genre, colour, etc.. As an example of what I’m hoping to set-up, you can have a look at this:

I’m sure there’s a way of organising this, but I’m really just looking for a bit of guidance on how to get it going. My WordPress skills are only intermediate and I’m feeling a bit stuck. It seems like it’s really the multi-site element which makes the whole process a million times harder, so if anyone has any ideas I’d really appreciate your help. Thanks :slight_smile: