re: Help me ovethink things. Backyard Woodshop Flooring.

Personally, I'd go with 3/4 inch tongue and groove treated plywood for the subfloor. That way they lock together and no need sealing the seams.

How high will the piers be off the ground until you reach floor level. Like mentioned, if real low, do some thick plastic over the ground for moisture abatement. It won't cost much for the peace of mind.

Also like already mentioned. Cushioned floors will be comfortable on the feet if you find yourself standing doing shop work, but moving big tools around if on rollers will not be much fun because wherever they sit for a while, they will settle into the rubber.