Progress report... For once, things happened just they way they were supposed to happen!
I was able to get my tractor started, with the help of Debbie's hair dryer. The ignition switch had gotten some water in it, and it froze solid – I could insert the key, but not turn it. Sixty seconds of hair dryer on high did the trick! Once started, the tractor made short work of covering the remaining uncovered bits of water line, which means that we were ready to turn on the water to the barn. I even got to hook up the snowplow to my tractor, and to try it out a bit on the inch or so of snow we have on the ground. It worked great!
Then a great big truck drove up, and the insulation team went to work. They filled the voids between the first floor ceiling and the two roof sections above it with fluffy fiberglass insulation. That completed the insulation work on the first floor (we've a bit more to do on my second floor office), which means the barn was ready to turn on the heat.
Just as the insulation guys were finishing, the plumber (Nate M.) showed up to finish the work on the barn's heater. We turned on the water supply from the house, and he started bringing up the water systems in the barn. In short order he had the toilet, bathroom sink, and water heater all working. Next up was the heating system, which has three zones with size heating loops apiece. Each of those loops had to be bled free of air, so eighteen times he forced water through a loop until the air was gone, then moved on to the next one. After that, he set up (through an on-screen setup program) the boiler. By the time he left in the afternoon, we had 72°F water running through the heating loops, and it should gradually increase until the temperature in each zone hits 60°F – probably by Christmas Day. The thermal inertia of the concrete slab means that we can change temperature only very slowly – a few degrees per day.
It looks like we'll be able to work in the barn all winter, just as we'd planned. Yay!