How many residents use the computer? Also, what is the average level of computer knowledge?
You can create as many accounts as you like, as long as you have space on the hard drive.
To my understandin, each User account uses about a gigabyte of hard drive space, and that is before the User starts saving documents, pictures, etc.
An AV program you may want to consider is avast! Malwarebytes' Anti-Malware is also a good choice. In that kind of scenario, running an online scan
on a regular basis would not be a bad idea. Free Online Scanners