1. The merchant will supply UPC codes.
2. UPC codes will not help you narrow down a category. Instead UPCs will return just 1 product because UPC's are specific to a single product.
3. No, UPCs will not come up in the search results.
"Taylormade Drivers" is not a single product. It's a group of products (ie. a category). Customers don't know UPCs so it's useless to allow them to search via UPC.
Personally I think you've done a very good job of narrowing down your selection of products and organizing them very well!