While there may be exceptions in some categories, AFAIK, there are no minimum quantities that can be shipped to FBA, at least in regards to rules. I sell books, and only very rarely ship more than one copy of a title at a time.

You may, however, run up against cost effectiveness on your inbound shipping. Sending a 50 pound box costs little more than sending a 10 pound box, so if you are sending small quantities, such that you are sending smaller boxes, then you will have an increase in your costs for the entire transaction (many people overlook inbound shipping when figuring out FBA costs, but they are real). Although I imagine that "workout sets" will probably be hitting those weight limits/box without requiring huge quantities.

Regardless, sending just a few to see how it goes is a good idea. Keep in mind that, if it goes well, we are hitting the busy season; a larger shipment sent in October may take several weeks to get fully available to customers, so plan ahead and watch carefully.

(and of course, pay attention to your costs; there are a lot of them, and they add up; but higher prices and faster sales can make up for those)