Have you looked into doing just that? There are a number of options and more arriving all the time.
https://ghost.org/docs/api/v2/gatsby/
https://ghost.org/docs/api/v2/gatsby/
> Of course I'd like a static website for deploying, but I'd love a web gui which acts as a frontend for such generators.
If you want such a gui on your local machine you're not much more than a few commands away
npm i -g ghost-cli
ghost install local