I'm using the FaaS to collect payment for registration to an event (where registration is handled externally; we are not using C&P Events this time around).

When someone registers for this event, they select a level of participation and are then redirected to our payment site. The form should then reflect that choice, and be ready to accept payment information.

These levels of participation include incentives, like membership to our organization, or a t-shirt.

We need to track t-shirt sizes.

I think that using "Products" in Salesforce, and connecting those via SKU in C&P, is the way to go.

Could someone point me to the next step? What do you do after you enable products for opportunities?

I'm modifying the complete FaaS example in Brackets.