Hi Christopher,
Please answer my queries mentioned below regarding your requirements so that I can give you best possible quote. Plz mail me at brenda.cis40 (at) g mail (dot) com
1) Have you already a module with back office feature or you need a module from us?
2) Do you want to filter products from all categories with Purity fields of products?
3) What is the mean of product.metafields.namespace.purity ?
4) Can you let us know that where you hardcode in the values 85 to 95?
5) Can you give us any reference site where this type of functionality exist?
Regards
Brenda