Thank you, it is incredibly motivating to receive such praise for our work so far, and makes the time that we've spent on the game feel worth it.
I'm very happy to hear how much you're enjoying the game and it's characters and I hope that we'll continue to provide a story that meets your expectations going further.
Now for your questions:
1: "Does the version of the game that I will have access to by paying already have much more content than the current demo?"
Yes it does, however, the additional content right now is the Bakery route. As time goes on the paid version will have more and more content than the Demo does.
2: "if I eventually have access to the most updated version of the game, will I lose my saves?"
As long as the saves remain on your computer you should have access to them in future versions. Still there is always the chance that we made add something in a later version down the line that will break your saves, but there are currently no plans for overhauling anything that may cause that.
So all in all, right now if you enjoy the content in the Bakery route and want to proceed past it's "Route-lock" then the paid version will have that extra content. Still, the $25 version on itch will give you lifetime access to the latest version (A month after Patreon release), and is similar to an early access in that regard.