> I would like to build an app that's a series of games, that are all related. I want to use the freemium model, with a one-time payment. No ads, no subscriptions; once you pay, you own the entire game.

That sounds a lot like old-school shareware. The free version was a full copy of the game that only included the first few minutes/hours of the missions/worlds/characters. Paying got you the whole thing.