Also things to consider if an official or unofficial guild is decided upon or you simply make one on a whim...
-What faction would the guild be based on? Alliance or Horde? Some people like one over the other. Some may like both but prefer one faction (like I play mainly Alliance with a few hordie characters). If one faction is chosen, will there be a sister guild or the like for the opposite faction? This could be important, but only really major if already established members want to join but differ in preferable faction, otherwise not so much.
(though Blizz should really just sort of get rid of barriers with faction to extant already, like in grouping or with guilds. I mean Azeroth's already had so. many. world-ending catastrophes, invasions, and big-baddies we've had to band together to fight back before. And things like the Legion's expansion where factions are "sort of splintering" and classes coming together in unison instead and I believe a "mercenary mode" being worked on for PvP(?) where you will join battlegrounds with the opposing faction, and even shared auction houses I believe at WoD's start, so why not just tear down some of the other barriers? Makes sense lore/gameplay wise, especially with the huge drop in subs. They can still keep the factions just allow more intermingling amoung server populations)
-Secondly, what server would it be stationed on? What's it's population? (High, Medium, Low? Does it get full often? Do you like heavily populated servers?) What's the ratio between Alliance and Horde players? (Relatively similar populations? Or is one more common than the other? Like Proudmoore on NA realms is mostly alliance players.) I guess cross-realm technology and stuff have sort of made this a moot point but I don't really know how large it's effect is. Also is it a PvE server? PvP? PvP-RP? RP? I'm not interested in WoW PvP and hate ganking so I only play on RP or PvE servers. But do others like otherwise? (like world pvp could be prevelant on pvp servers, though from what I hear thats been dead since Wotlk)
-What realm? North America? Europe? Oceania? etc? Important for timezones if you want people to play together or set up things like meetings or raid nights or whatever.
Ehhhhhhhh... I'm probably looking to much into things/probably just stating things I tend to do before settling down to play on a server, but meh, thought it was worth mentioning. Probably everything (besides the faction bit) is only relevant if its mostly people who already frequent the forums play/join the guild, and there's probably less of that happening/being as important as players who already are on the server that possibly join. Plus a guild would probably just be formed on a server someone already plays on, or they just join an already established guild a Topian's apart of.