Yes, my app would be a lot like Zettlr but tailored specifically to blogging, with the publishing built-in; it appears to me that Zettlr is more a generic .md editor.

FWIW: my app isn't Electron, it'd be native macOS, that's just my skillset. Maybe i should just use Electron so it could run on windows/linux to be honest.

Yes, the plan would be for the blogger to get their own domain. Bloggers generally already do that when setting up with Wordpress so i don't think that's a problem.