@elbie47
As @briankasingli and @arpitvarshney mentioned, the primary way to solve your problem is to provide correct access restrictions to the users . You have to create correct set of groups for your content authors/ managers and set permissions for them to the correct set of pages so that they won't be able to access the pages which they are not intended to. Rest of how to create groups and manage the same are mentioned in the above answers.
Noe coming to your other question of Project vs Page , project is nothing but a grouping of your resources. I am not sure if you got a chance to go through this link https://docs.adobe.com/content/help/en/experience-manager-65/authoring/projects/projects.html . If not , please read through and it might give you a clear overview and understanding on projects. Even while using projects, the permission control should be done via users and groups.
As mentioned in the about link
When you create the project and add users to the various roles, groups associated with the project are automatically created to manage associated permissions. For example, a project called Myproject would have three groups Myproject Owners , Myproject Editors , Myproject Observers . However, if the project is deleted, those groups are not automatically deleted. An administrator needs to manually delete the groups in Tools > Security > Groups .
