Ran the new rig through its first complete brew today. A delight! Everything went very smoothly, with only minor hiccups.
The mashtun's heat-retention was probably the biggest question of the day. Happy to report that it's brilliant. Less than 1º temperature drop over the full hour of mashing!
Burners are fine, though I may try swapping them around for a brew sometime, just as an experiment. I'm pretty sure the 2 burners are pretty unequal, and I don't need such a massive flame under the boiler; once it's reached a rolling boil, only a very tiny flame is needed to maintain the boil.
Pump behaved admirably. The drainage plumbing bits I added are unnecessary: Once the mashtun-drain is disconnected it works just fine as a drain.
The only thing that went wrong was an unexpected leak of coolant-water from the chiller! This after testing it 3 times and not experiencing a problem yet. The only challenge was to keep the leak-water out of the cool wort, since it is dam-water, so something I definitely don't want landing in the wort.
The crush was terrible, though, so very poor extraction. OG 1.030! OK, so I have a week to solve the crusher issue while this batch ferments out.
All done, including cleanup, in a fraction over 4 hours. Pretty good going for a first run, and possibly the most relaxed brew day I've ever had.