Anchoring an outbuilding -sequence of events?

I mentioned yesterday that I want to build a pump house for the pond. My original thought was to build the frame (4x4s) first and then cement the legs in the post holes. But after doing a little reading, I'm not sure this is a bright idea. Because it might be hard to get the footings level in all four post holes. It would seem better to cut the posts to length AFTER they are hardened up. I could still join the posts together with the crossers while the cement is soft to get the horizontal spacing I want.
(The above seems kinda obvious now, but any countervailing opinions welcome)
I know I could use saddles, but I've not read good things about PT wood and metal. I'm also concerned about the leverage the water wheel may exert on the wood in the saddles. The pump house will also have about a 1,000 pounds of water inside.
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