It's not the most important thing to consider, but I'd still add them. If you can help Google to understand what your product is about that's something you should be interested in.

We can't really answer the "how" question without any idea about the technical background of your site. However, it's not rocket science. I'd find another webshop with micro formats, check how they've done it, confirm that their implementation matches the specs, and implement the same stuff on my site.

Several platforms support this out-of-the-box.