Many thanks:
1. I don't want the devices connected to the output of one dropped supply.
2. Good.
3. Now not an issue maybe as I've pressed into service a 5amp 13.3v input supply.
4. Placing the diode after a regulator would surely only be appropriate if all devices were being supplied by one regulated 9v supply.
As mentioned, without some form of isolation (immediately after the 13.3v supply) I'm concerned the respective caps for each circuit would be in parallel with each other. But perhaps this is not an issue (at least with the electrolytics) as the values would be added?
I guess the main reason is to prevent the 7809s from being connected in parallel which, I understand after undertaking web searches, is a non-starter.
I note your comments regarding using five LM317Ts and have in fact noticed some very cheap small complete functioning modules on eBay utilising this chip but I would prefer to us components I have in my junk box first.
I would be grateful for your further thoughts on this project. Thank you jiripolivka.