Why are you making a job bigger than it has to be! When I hired a fence contractor they came in dug the holes by hand. Set the post, added bag of concrete then poured in some water. No cement mixer!
My SOP for most (not all) posts as well. Bore the hole, crumb it out, set the post in (I coat the bottom and sides of the post that are in contact with the ground with liquid driveway sealer even if PT posts (they last longer), drop in the post, add one or 2 bags of Quickcrete and cover with soil. The Quickcrete allows you to easily square the post and ground moisture will set the Quickcrete, no water added unless the soils is extremely dry.