In my opinion, this game did it right. https://tarkovsky.itch.io/fumes Released a free demo, advertised a release date on Steam, released a cute parallel game called Rust Mites, an hopefully will be keeping the demo free after the release. Because of the long demo stage, it has a small and dedicated community who are huge fans and will likely buy the full game. Parallell games are a neat idea. Make a minigame with the same graphics style and roughly the same content, and release it seperately. That way you don't have to ask "how much free is too much?" Longtime demo players will get a completely new experience once the game releases, while giving the community something to play and wishlist if they like it.