I didnt read all the responses, but heres what we do. Similar to the tankspot video, we split into 3 groups during the transition phase. MT and melee in the center, Ranged on both sides, OT on one side.
There should still be 2-3 ghouls up chaining the disease. So, the OT should be more than 5 yards from anyone else, and when the disease kills all ghouls, dispelling the OT will remove the disease, getting rid of the lich kings buff.
Also, we pop heroism during the transition phase, so there's only 1 spirit left, sometimes two. The OT (Without the spirits) picks up the lich king until a tank switch is necessary. By then, there should only be 1 spirit left, if any. The tank with the spirit and the lich king will have to pop cooldowns.
To help with the valkyr : If you have any warlocks, keep them at the edge during phase 2 (or three, whatever you call it. the one with the valkyr). They put their demonic circle down, and when they get dropped by the valkyr, they can spam summon, and pop back up. I have heard, but not attempted that a hunter can disengage to the same effect.
Good luck