Those are a good start. Cost, networkability, what programs are available are very basic starting points. What other companies that communicate with you can also influence things, for example if everyone uses Microsoft formats that is a contributing factor.
Some things I find important in an operating system:
1) Ability to run the software that is needed
2) Updates and security patches
3) Ability to connect to networks
4) Provide a file system
5) Provide maintenance tools for the operating system's health
Your teacher may be looking for something else though, so try to remember specific things the class covered.
What do you think about the other questions?