I understand your desire for closed source to maintain control of your revenue stream, but I believe that you’ll find most Fediverse folks adverse to closed source. Many associate closed source models with a lack of transparency and a loss of control. A small tool like yours might not run up against that kind of opposition simply because it is small and does not handle a lot of data.
I do like the pay what you want model. It's helped fund support for open source projects in the past so there shouldn't be much pushback for that.