Hi all,
I haven't had much time to collect information and post it here, but I haven't been completely idle. The manifold is hooked up, the old furnace removed, and I've had a bit of a hard time (understatement of the century!) in getting the system filled and working with the new water heater.
Here's the story of the last few days:
Adventures in home improvement: Oh dear God
Long story short, there's some bad luck, probably some bad decisions, and a faulty water heater involved in creating what I can only call prime sitcom material. I figured instead of only reporting on what worked, I should also post about the complete disasters and failures, so that's what the wordy post I linked to is all about.
Hope this helps someone avoid similar problems!