All WHM would need, imo, is one buff. And it's a simple one, one that's been staple to the WHM job through the series.
Haste/Hastega
Idk how long it should last or how long its CDs could be. I'll leave that for you guys to theorize. But srsly, I feel it's all a WHM would need for a buff. And like I said, it's been a staple WHM spell since ever.