Hey! Just in case you haven't made up your mind already, I recommend you check out Hopi (http://www.hopixsyon.com/). We are a good aligned, mature tribe that focuses only on Xsyon (not a multi-gaming guild). We have a solid member count of at least 20 active, although we've been growing so much lately it is difficult to know for sure.
Regardless, when I first purchased Xsyon I was looking for basically the same thing you are, and I've found that Hopi is exactly what I wanted in a tribe. If you decide to go somewhere else, no problem, we hope to see you in-game. Good luck!