It's only as complicated as each participant wants it to be for them.
Start with what you'd like sent back to you, such as specific varieties, mystery varieties (within a specific "type"), and how many total varieties. The average participant usually gets about 100 different tomato varieties back, unless they specify less (rare), or more (imp)
.
And, peppers, beans, veggies, fruit, and flower seed is a smaller part of the swap. These are much harder to meet requests, so I post a list of what comes in (sometime in November) and participants chose from that list.