Thanks for the info, Phil1977!
One really last remark: Have you thought about fuses?
I have. I've been assuming one fuse per output-to-device, regardless of whether I'm going with a single 12V step-down or your suggestion of one per device. I've got a fuse for between the battery and the inverter I'm replacing all this with, but I'm lame and haven't installed it yet. My "excuse" the inverter has a 60A fuse on DC input side and the DC cables into the inverter are 6AWG, and my load is 300-350W max now.
One sort of "problem" is I'm building this a proof-of-concept with separate modules initially in a wood or plastic enclosure, but I eventually plan to build it as a PCB. I say that because the fuse situation would change.