Users and Groups

CentOS 7, Virtualmin GPL

Hi.

I’m having a hard time understanding users, groups and their permissions, so perhaps if I set out what I want to achieve then someone could give me a guide.

With my last host I was logging in to SFTP as root, with password, and so able to navigate and edit all folders. I’ve read that this is not good practice, so on my new host I want to avoid that and log in to SFTP with keys as say User1 but still be able to navigate and edit all folders including those owned by root and other Users. (As I write this I wonder if this is actually any more secure, apart from the use of keys, than logging in as root)

By assigning another user, say User2 to User1’s group I am able to navigate all User2’s folders but cannot edit. Perhaps I should create a new group and add all users and root to it - what would I do then with making this group as Primary for users?

Additional info:There will be one user who I do not want want to give global access to. User1 has sudo access and is a member of the wheel group.