Does buying the game on itch give access to subsequent updates at no further cost ?
Also, does the full version include all patreon features, part of them or none ?

Regardless, great game, would be happy to contribute after all this time following it.

Yes, buying the game on Itch gives access to all future updates for no further cost. Patrons still get early access to new updates for now.

Once the game has a finale and leaves its early access period, I plan to open the patron features to everyone (mostly the ability to Reminisce previous scenes) and publicize the cheat menu password.

I don't currently have any plans for paid expansions/DLC. I can imagine a world where I charge for some sort of chunky story expansion, but it feels unlikely.