To me the ideal solution to Problem #1 would be setting up a “Conditional Field” as proposed in this thread: Conditional field - Creating a 'Flexible Content Field' (like 'Advanced Custom Fields' wordpress plugin)
From my in depth experience with WP I can say this kind of functionality is extremely powerful. I wish I had the ability to help get this into the Grav core as it would be a huge leap in ease of use (for the non-dev users we are often handing off the admin to).
Also, @lilive from my testing you can indeed have a modular parent page that also has child pages. I’m not sure why the documentation says that. Maybe it’s just not recommended as it could be confusing to other admin users?