Update:
Well, on Sunday, the wife and I worked some on laying out the shop. First, we pulled a string line along the west property line so we could square the building up to the world. Then we flagged the approximate corners where we intend the building to sit.
After roughly placing the building, we drove stakes and nailed on batter boards so we could pull stringlines. So far, so good.
Next, we set out to square up the strings. We spent a good deal of time and struggled to get things to come out right. I hadn't expected it to be easy, but something seemed off. Eventually (after she'd gone back home frustrated) I figured out that the 150' open reel tape measure would stretch or seemed to stretch, so you could make a measurement come out to any number you wanted, just pull a little more or a little less. Worst was any measurement along a stringline up off the ground, since you had to pull quite a bit to take up the sag, so getting a measurement to repeat was nearly impossible...
I got things close enough for hole drilling I thought, considering 18" holes for 14" footings and 4.5"x5.5" poles...