We're going to be transitioning from a small, outdated CMS that's no longer supported, to WordPress for our new CMS. Our old CMS allows us to restrict access on the back-end so that by default User A couldn't edit content created by User B. Our old CMS also allows us to create teams/groups, so that if a group of content creators wanted to work together, they could share access to content while preventing others from accessing it. Basically we have a team of 50-100 people that would be using WordPress and don't want them stepping on each other's toes.
Is there a way to do this in WordPress? We're planning on running one instance of WordPress (not multisite) and posting mostly pages (not posts). The built-in roles don't seem to be able to handle restricting access, nor creating groups. I've searched and found the plugins User Role Editor and User Access Manager, but was wondering if we were going about this correctly, or if there was a better way to do this.