One way of thinking of users are actual accounts which a person could log into on your server.
But a more common view of users, which you should get used to for administration, is more like a system role.
For example, if you install apache, you will see apache running as 'http' or 'apache' user. That is a legit user on your system, but noone could login as 'http' or 'apache'.
Users should not be thought of as a scary thing. It is okay to have a lot of different users on your system. The real keys to the kingdom are in the root access and the ability to use sudo to access other user accounts.
As long as you keep root locked down and secure, and don't give anyone else sudo access, you can have a lot of users and stay safe.
Just remember files execute as the user who owns that file. So if you have a script in a file owned by root, that script could be very powerful because the commands it runs are carried out as if root were invoking those commands. The file inherits the same privileges, but also the same restrictions, as are held by the user which owns the file.
This is why apache runs as 'apache'. In a way, it protects the rest of the server if 'apache' user ever got compromised. That is just an example, but the general principle applies to the big picture.