I get the impression you are looking for something higher-level than the solutions being offered to you. Something like Smartfox Server or Photon would serve, but unfortunately they aren't free.
I could use any message queue for messaging, but I was hoping to get some added value besides packeting over TCP/IP. Message queus also tend to lack a security layer, which is a big deal over WAN.
Thanks for the links, I'm a complete newbee in multiplayer, so I was unaware of these.
Regarding Smartfox, 100 concurrent users should be enough at first. I see that smart-fox community edition supports it, but I can't find the license on their site. Do you know if I can use the community edition in a commercial game? Also Photon's 100 users for 10$ might also be fine, since if I use my own I'll probably pay ~10$ for hosting.
Also, what do you guys think of the Google offer I mentioned above? I cringe at the thought of forcing people to use Google+, but it looks very easy, and very robust. Also, I couldn't figure out the pricing.