How does Shop Pay installment and return policy work?

Payments + Shipping & Fulfilment
1

Hi, I need clarification on a few things regarding Shop Pay:

  1. If a customer makes a purchase using Shop Pay, regardless of what length of time they choose, do I ship the item right away or wait until all payments are made in full? ie: if they choose a 12 month payment plan, I ship after the 12th payment is made?

  2. Am I paying the Shop Pay % for each and every installment? ie: Am I paying 5.9% for every single installment payment? So if they choose a 12 month payment plan am I giving Shopify 5.9% of each payment?

  3. I read somewhere that there is a way to refund Shop Pay payments. I offer a 3-day return policy. Does my personal shop policy supercede a Shop Pay return policy or do I have to abide by what appears to be a very long return period through Shop Pay?

Thanks to whomever answers the above questions!