If you're only going to be doing it with a few friends, pretty sure you could use hamachi. I wouldn't be able to give any pointers on that. In the past when ever I did something similar, I would just open ports on my router to allow traffic to the VM. But as Riotoka said, please be careful if you decide to go public with your server.. It's been an issue for a very long time, hackers/ddos happens frequently with FW servers.