Front end authentication on an entry and its related entries
From experience, in terms of ui/ux AND ease in front end stages, If you can do things the other way round, do that.

So attached entries to users basically. When you have a new user, you add entries in one place vs adding the user on every single entries which, if you have loads of could turn into a bit of a mission.. You'll find this way round easier to maintain, in the front end, you can just access related entries through the currentUser very easily instead of going through entries.

This is my personal preference based on recent experience but I don't know how much flexibility you have in terms of development so it may not be possible for you.