I have a SaaS app aimed at small businesses, and I am considering an affiliate marketing program to help me reach customers, but have questions:
1) It's absolutely normal for a business to pay commission on any one of the options you gave, here are some of the thought processes that go on in that decision:
2.) Again, this is a viable option assuming you can justify it with knowledge of your business. My suggestion would be to leave that option out unless it's a precedent set by competitors of yours already. I would much rather have paid my one-off commission or just continue at the affiliates converted rate. After all, if a customer "upgrades" a plan it is most likely YOUR work and success that led to that not the affiliates.
3.) Might need a little clarification here, but there are plenty of plug-n-play affiliate programs such as ShareASale and HasOffers that let you build one to tack onto an existing site.
I can't say enough that the point here is to HAVE DATA. Have an understanding of what you can afford or in lieu of good information just fail safe. Good luck with the app!