I have a 10 box team set up now. I do NOT use one key to do it all, I maintain control over everything possible, and it works. I play with all but 2 classes regularly, and the two I'm missing (warrior and rogue) I actually have sub-ins for in case I need them. I got a rogue set up to replace my second tank on any fight where I don't need two tanks, and a warrior in case I ever need a spell reflect. So, yes, I am playing a very much multi-class team.

Melee classes always go on the main window per screen with their own mouse. I have two screens and two computers. Everything is based off of the tanks or melee. I would only use a max of two melee at one time. The tank in "party1" is the priority tank who gets assist, but the tank in group 2 has his own mouse to tank another mob elsewhere. This requires occasional splitting of attention, but once the mobs are positioned I can tank and heal easily and using one keyboard for everything.

DPS all have a short castsequence on "1" which does their main "cast bar" moves.

DPS all have various instant cast moves set up on 2 3 and 4. 4 is mostly used as an interrupt button. Earth Shock, counterspell, etc. If applicable. This is staggered in case I need multiple interrupts. I have alternates set up when I hit shift, like the warlock will blow soulstone moves when I hit shift with 2,3 or 4.

F1 is used for the DPS' "BEST" spell for when I pop their trinkets, which is set on a remote key, = and -. The tanks also use F1 for hammer or execute when the mob is low on health.

Shaman have totems set up on F3-F7 keys. No one else uses those keys at all.

7 and 8 are AOE moves. I have a lot of targetted AOE, which I can click each window and cast within a few seconds because of how I set up my windows.

The number pad is my main healing section. I have all sorts of healing macros on these, mostly for my tanks. My priest healer uses AOE heals to keep the team up when everyone takes damage, but I also have keys for EACH member of my raid set up on the U-P keys in case any one person alone needs a heal. I have EMERGENCY healing keys on the Home, End, Page Up and Page Down Keys. These will cast Lay on Hand on a tank OR make the elemental shaman do a /stopcasting and chain heal.

As stated earlier, all tanks have direct mouse click control, but they also have keys on Z to / keys along the bottom of the keyboard. So no matter which tank I'm focusing on, I can still hit those keys and effectively tank or DPS with the others.

QWEASD also moves the main tank, but arrow keys can move everyone else.

I remember all of this off the top of my head, so I guess I have a good memory.