Well, this week was our first ever attempt at Kara as a guild. We had a few members who had been through it before, who had left other guilds and reformed ours when my fiance and I started playing again, so we have an idea of how to approach each boss, just not the practical experience. Our core group looks a little like this:
1x Hunter (Myself) - Marksman Specced
2x Shaman - 1 resto (fiance), 1 elemental
1x Priest - Holy, of course
2x Warrior - One prot, experienced; one arms, actually not a guildy, but his alts are all in our guild so he off-tanks for us - crazy gear.
1x Rogue - No idea on spec, but they are very good
1x Warlock - Affliction specced
We downed Maiden the other night with an extra holy priest (who I swear phoned in the whole run - an ex-guildy who we brought along just for another healer, but who I doubt will ever be coming again), and extra warlock (also affliction).
Had our warriors and rogue triangle tank her, with the healers directly behind the melee'rs. The priests handled the warriors, resto shammy on backup/raid heal, elemental shammy kept grounding totem out to eat holy fires when possible. Rest of raid dps'ed from afar, while keeping in LoS of healers. Only real issues we had was a slight shift of her position which kept a healer from landing in the Consecrate during repentance, which led to an eventual wipe, and once our core 'lock pulled aggro too quickly (he realized too late that he had unloaded too quickly), which also wiped us.
We subbed our frost mage and holy pally in after the non-core priest and lock had to leave, leading up to the Opera fight, but after one wipe (mage kept trying to alternate dps and scorching Strawman), Roar fear-bugged and we called it quits.
Our main issue right now is that most of us aren't even heroic-geared, as about half the group hit 70 a week and half or so ago, right before we decided to head to Kara. The real exception is the MS warrior, who's geared in at least Kara gear or better, but who is committed to making us learn the encounters ourselves (and it's not like one person can make it for a group - break it, certainly, but not make it). Considering that, we're doing pretty well, and gearing up quickly. We have a pretty good class selection, too - our mage and pally just got attuned this weekend, and we have a feral Druid who will have hit 70 this morning, so he'll probably be attuned soon as well, and taking over off-tank duties.
As far as recommendations on that priest, either he's pulling aggro too quickly by massively overhealing, or he's eating up Holy Fires that he should be dispelling immediately. Not sure if decursive would really help him out, but if you have a shaman, consider having them toss a grounding totem next to the dude. If they're dying when trying to get Repentance off inside the consecrate, then it's probably a gear issue, and they need some more health. Either way, it shouldn't be too much of an issue if they keep alert. What's your raid makeup like?
Keep in mind, we've downed her just the once, so I'm not claiming to be an expert on the encounter.
~kov.