as said above, expedient 3 is either a random roll on a piece or you get it from Mother when the next rotation comes around.
major essences would be VOP, Lucid; MInors would be Breath of the dying, focusing iris, Formless void, conflict and strife (Lucid or VOP as set and forget minor based on what your major is).
your ideal essence setup for cleave/AOE: 3FP/2RH/1CC + VOP Major
single target setup is trickier because destro isn’t exactly a god at single target like we are at cleave. Probably something like 3FP, 2HOD (raid trait), 1CC with Lucid Major. I haven’t seen anyone using worldvein but that could be due to having the better options already available, so while i won’t discredit the post above i don’t see it as optimal, but could be a decent stand-in for a short while.