Random question ever think of selling your voice library as a product as well? You can put "Powered by" for free users and for paid users it can be shown in an "About" page instead.
We’ll see it’s a ton to build as a side project.
If you can make certain parts of the code reusable it will be for the better code wise too. But you know your situation better than me, just sharing a simple idea. Good luck, I would love to learn about ML more, but I don't have the background I perceive necessary to pursue that. Plus I've got other things I want to master (it's an ever growing list) that I need to focus on.