fwiw: TestFlight, as I anticipated, seems to be a good beta user (team) management platform - and you have to bring your own team. The setup was really fast and the App setup tool pulls certain info from the APK file.
TBF has an approval process (expected) and a freemium model. You can select to fund a test campaign starting at $0 and how many users you will accept (you select users after they apply if the test is public).
If folks are interested, I can keep this post updated with my findings - based on any suggestions you might have (so keep the ideas coming). I know sometimes you're not ready for certain details - but it's cool to go back through the discussion lists.