How to limit the pages shown in the page manager to those created by the logged in user?

There is a way to do this code. You can hire a dev or check out this plug in: https://wordpress.org/plugins/user-access-manager/ It looks to have the features you need.

If you are interested in diving into the backend, the place to get started is by building custom page templates.
Here is some good resources on page templates:
https://developer.wordpress.org/themes/template-files-section/page-template-files/page-templates/

and the code to redirect non admin users away from that page:

https://codex.wordpress.org/Plugin_API/Filter_Reference/login_redirect

I hope that helps!