As explained in the project's webpage, the only requirement it's (not too variable) static IP address and an adequate bandwidth. NTP Pool Project historical data suggests an average traffiic about [10,15] kbit/s with peaks of about [50,120] kbit/s. Joining it's easy and you can monitor performance data of your server on the administration webpage which can be accessed after registration.
A quick warning before you rush and public your server(s):
Finally, I must emphasize that joining the pool is a long term commitment. We are happy to take you out of the pool again if your circumstances change, but because of how the ntp clients operate it will take weeks, months or even YEARS before the traffic completely goes away.