Is there a way to show products that may be of interest when choosing one product (similar to the way Amazon does)?

You could relate the parts inventory table to itself to allow for specific linking of products to each other, Or you could create a formula field that would present a link for each line item. When clicked, the link could query the parts inventory table for items sharing the same category or sub category, or any sort of classification data fields that would associate 'like items'. 

This is a very fun and interesting problem to solve and I've done it both ways. Let me know how you solve it. Good Luck!