I talked with Pheebe with Shadowcraft and they would love to instance with us. But alas, they are a really small guild, with a handful of 60's, a fraction of what Redeemed has. We still need more people.
I think a recruiting post on stonemaul is grand idea, especially if it hilights both the social standard of the guild (Christian) with end game participation and that we are looking for a few good people to help with Onyxia or looking to partner with a likeminded guild to run Onyxia.
As for gear, fire protection potions are more important then fire resist gear. The only time you really have to worry about fire damage is duirng stage two IF onyxia does her deep breath, which she wont do if you keep a constant DPS on her. Stage three, which I've only experienced once, seems to be a matter of repeating stage one, dealing with the new agro list wiping fear (dwarf priest for the win) and dragon whelps being popped (assigning two groups to AoEing them down). And if we can pull a few experienced people that will help a bit as well.
It can be done with UBRS and Dire Maul level gear because if you can keep her from deep breathing during phase two, you don't need FR gear. All 4 trash mobs are simple. They work just like the Baron Ghedon fight, one tank, rest ranged DPS, if you don't have ranged DPS, help heal the tank or watch the light show.
A weekly Ony attempt is a great idea. Get 35 to 40 people who will show up every week to attempt it twice a week until you get it, probably won't take more then a few weeks to get her down, and then down consistently afterwards. All teir two helms drop off her, and she drops two helms each time, also she drops miscellaneous weapons, trinkets and the like ranging from superior to epic plus she drops her head which starts a quest for a really good FR item (If I recall correctly).
For guilds that have Ony on farm status, its a 20 minute or less fight.