You need to have good, clean power, meaning you need a UPS and perhaps a generator to deal with power outages. This includes air conditioning. You also should have multiple locations in case there is a problem in the area.. You need multiple connections to the Internet, in case the primary connection goes down. You also need staff who know what they are doing and able to deal with problems, technical people.
You can create accounts on individual servers or you can use a centralized service using something like LDAP, NIS or Active Directory. You need to be able to select which machines the accounts can login on. It also needs to be easy to deal with since otherwise it can take a lot of time. Quotas will take care of the disk space. There should be packages which can track some of the network usage, but that gets complicated. Network switches might also provide some control in this area, but there is a lot to track (web page usage, file transfer, etc.).
You need to have a good firewall which can be created from a Linux box or getting an expensive network switch (ie. Cisco or other similar switch). You need to be able to block IP address and monitor usage to deal with problem access, such as DOS (denial of service) attacks.