@SamP20 There are some CMSes out there that are basically just frameworks where you can define what fields and metadata you want different post types to have. How close does that get you?
@SamP20 Dunno! All my backendy/CMS experience is with LAMP stacks; so I'm thinking of things like ExpressionEngine, Perch, and WordPress w/ ACF. Don't well know if there's anything that matches your specifications.
@kimpegasus Are there any that include a comment system too? I don't really want to rely on 3rd parties like Disqus. Also MongoDB backend would be nice too