Assuming Windows XP ...
1- I don't think there is any easy way to automatically sleep the computer, but you can use the shutdown command to hibernate the computer ... shutdown /h
. Put it in a batch file and set a scheduled task.
2- I have found Wake-on-LAN to to be a lot of trouble. Generally, the BIOS and the NIC have to be set to enable WoL, and I have found that some NICS/PCs wil wake up on other traffic than WoL packets. I would avoid it if the idea is solely to have the PCs alive when people arrive; restarting from sleep/hibernation is pretty fast.
3- If there is a Windows domain I believe that shutdown/sleep/hibernate and wake-up/startup can be controlled through Group Policy, or at the very least the scheduled settings and scripts can be automatically deployed.
4- Although sleep/hibernate are pretty good at not losing data, I would make sure that Office app autosave settings are enabled, just in case. For Microsoft products, these can be controlled via GPO as well.