Recommendation for Plugin

If I am hearing you correctly, WordPress already has that:
https://codex.www.ads-software.com/Roles_and_Capabilities

Someone with an Author account can only add and edit his or her own pages. And if you find the Author role still has more permissions than you would want, this plugin can let you manage those or even make a new role, cloned and modified:
https://www.ads-software.com/plugins/search.php?q=Members

Also, you might want to add this at the bottom of wp-config.php to block anyone and everyone from the Dashboard editor for themes and plugins…

# disable file editing from Dashboard
*/
define('DISALLOW_FILE_EDIT', true);

…then set the permissions for wp-config.php to 0400 as a security measure against hackers that might try to get your database credentials from there.

Hey. Role Scoper seems like it’d meet your requirements: https://www.ads-software.com/plugins/role-scoper/. You can use it to allow/disallow users access to pages/posts on a user-by-user basis.