One of the largest open-source Rails apps has all of those features: Canvas LMS[1]. It uses Switchman[2] for abstracting the multi-tenancy logic.

Their approach has scaled to millions of concurrent users, but admittedly not helpful if you’re looking for a guide since the code is buried in a legacy monolith.

Part of the reason there isn’t a generic guide to this is that multi-tenancy is probably a premature optimization if a generic guide would be helpful. Just use nested user accounts to accomplish your business logic. By the time you really need true multi-tenancy, generic sample code won’t be much more helpful than the docs of the various plugins like Switchman.

1: https://github.com/instructure/canvas-lms 2: https://github.com/instructure/switchman