When allowing anyone to create a account, should you use a custom account management process?

When someone creates an account, using an invite code, they will be a part of a specific group or groups if they have multiple invite codes.

No one should ever see content from other groups, only the specific group they have set as active.

Are there any reasons to use or not use WordPress' built-in account management? I don't want people to be able to edit WordPress or do anything outside of the groups they are members of.

I don't want to use any third-party plugins. I'm writing my own and have the foundation in place but just not sure how to handle user management.

Any recommendations?

Thank you.