Louis, I agree with Enno on all points. SQLite and RootsMagic would both be good choices, and a lot of the groundwork has already been done with SQLite Tools for RootsMagic. Like Family Tree Builder, there is also a free version of RootsMagic, which has very few limitations. I just don't know about the legal ...
Behold Database Plans - Forum post by geneatech in General Discussion - 16 Jun 2019