And this brings us to number four:
4) An audience relationship management system, ideally one with an API one can build against
Here's where you can really kick Patreon's ass in the market for alternatives, because Patreon's game has been slipping very badly in this area.
I just invented the term "audience relationship management" system, by analogy to "customer relationship management" system. Like I said patrons are not the same thing as customers. But if you're a creator you do need to keep track of them, and you do need to keep track of their payments, and you do need to be able to communicate with them.
Also you would probably like to be able to tell what's going on with your money: with the amounts pledged, the amounts received, the fees deducted, the credit cards declined, stuff like that. You might also appreciate some analytics.