The WHM should run 20'+ away from your melee shortly after the fight begins to avoid getting hit with Breakga. It's rare that it casts this but it can be devastating if your WHM gets hit by it, especially if it follows Breakga with Chainspell. After Chainspell has started, you can run back in and do Curaga because it will never cast Breakga with Chainspell up.
Fade makes a very noticeable difference for my runs (500~600 damage -> 150 damage). It's not necessary if you have a WHM in every party. Many of my sessions end up with some misc jobs in a secondary party without a WHM though. It's nice to not have to worry about healing them. I think I end up entrusting it (or maybe Fury, idr) most of the time anyways as I super revit between every fight.
These are good WHM-related tips! I just used my alt/mule to WHM some Neak for the first time the other night. The only troubles for us were just the things Snaps mentioned: (1) I was too close and got Breakga-ed on WHM once followed by Chainspell, which went as poorly as you might expect, and (2) one run we tried to go with 2 parties, one party with several melees and no WHM - they died (they also didn't seem to particularly care about eating Meteors to the face despite lacking party healing).
I think our setup was:
Tank party: PLD WHM GEO
DD party: WHM GEO(Idris) WAR(Bravura?) BLU(Tiz) SAM(Masa) and 6th who was some other DD, BLU or WAR I think.
Also had rolls-only dualboxed COR to drop Samurai/Hunter's on DD party then join the tank party to roll and stand still out of range. Magus/Runeist on tank just because, which was nice but inessential (didn't want to just leave the COR outside party, cause personal spoils campaign).
We were getting 2 kills before ~8:30 rolls wore, including time for the popper to go make new KI between fights. I'm sure non-Idris or switching any of the DD slots with any other reasonably competent/geared DD would be fine for wins too.