Back after being gone a while.

Brief intro. Im not new to the MB scene. First realy MBing I did was back in the mid 90's with Ultima Online, and since then ive MB quite a few games. Asherons Call, Dark Age, EQ etc. I started MBing in WoW about 3 years ago, pre BC. I didnt know anyone who MB other than a few people 2 boxing a healer and classX No one 5 boxed. So with my company discount and $2k I got 5 identical boxes with monitors and started "The Cluster" About 2 months or so after starting someone at work found the Xinns and I was weak sauce compared to that setup.

I did it all with software at first, I used synergy to use one kb and mouse. and some great UI mods when they did wonderfull things. Now its a lot easier with a keystroke broadcasting version of synergy and keyclone and ive reduced the hardware to just 2 boxes from five. the other boxes made great birthday/christmass gifts.

By coincidence the 5x that I went with was just like Xinn. 1priest and 4 mages. This group cut a bloody path through the original content a mile wide. I got them all to 60 and got bored, then BC came out and I waited a bit before getting it so it wasnt a land rush. Like before they left a path of distruction behind them, till ramparts. I could kill everything but that damned dragon mount.... anyway it got worse and more and more clear that massive DPS wasnt cutting it, so a year or more ago I retired the cluster. Now I fired it back up. with the tweeks to BC and stuff they are back to killing again, but as they get to 70, the old problems are back. Playing in Nagrand theres group quests I cant finish. Looking at the pattern I know the same will be in WotLK and I dont feel like dropping $200 on expansions to conferm.

Today the 5x communtiy is much greater and instead of experimenting im here to ask a few questions, because the 1 priest 4 mages I dont feel can be successful in end game pve areas.

Reading forums and watching vids for the last month I have come to the conclusion that A. I need a tank, Paladins seem to be the frount runners here being able to AOE agro easily. Second is a dedicated healer. and the rest is DPS.

When it comes to the dedicated healer you have a priest, druid and shaman. Im wondering if picking a hybrid healer (druid/shaman) over the priest later on will become an issue?

The next question is the 3dps. For me the simplest option is to level a paladin and remove a mage and ill have a pally, priest, and 3 mages. Would one be better off replacing a second mage with a Shaman or a warlock or some other 3dps class combo or a druid for more buffs?

The fewer classes you have, the easier it is to set up macro's.
If your dps is 3x mages, then all of your dps will be synchronized.
Mages bring very good dps and polymorph as a crowd control.
Different classes for dps bring more flexibility for PvE but become harder to coordinate effectively for PvP; with multiple mages already leveled, I'd try to create a fit with your existing toons.

As far as healers go, a shaman is a very good option, even elemental spec.
The totems are a superb addition to a mostly caster group, and the paladin (if that's the tank you go with) is the only one to use mana.
Totem of Wrath, Wrath of Air, Mana Spring and an Earth totem of choice.
If you have problems with any level of content, respec the shaman to restoration for a big healing boost, and all you lose as far as totems go is Totem of Wrath downgraded Flametongue (spell damage totem).
Since your mages are cloth classes already, and damage/healing and healing gear has been combined into spell power gear, I'd not go with the priest who is also a spellpower cloth user - Druid or Shaman are both good choices; priest is as useful as these two, but will compete for gear.

Paladin is the easiest multibox tank, but warrior's, druid's and death knight's are all very aoe friendly now.
I'd vote paladin for your team, but any can work well. Paladin/warrior/death knight are all plate users, druid is leather as far as distributing gear goes.
The Death knight will start off at 55th level, which might make it a better choice then the Paladin as far as getting into Wrath content sooner. It isn't that much harder to box then a Paladin and is also a very good choice.

I run a Shaman as my healer. When I was healing with a priest there were times where I'd look up and she'd be dead before I knew she had been hit. With my Shaman, he can be getting beat on by several mobs and between his grounding totems and his armor, my pally can run back and steal aggro off of him.

Tanking? I love my pally, but after reading what everyone is saying about DK's, I've been thinking about starting one and seeing their tanking ability for myself.