I am almost positive b) is correct. They didn't even allow this in Vista, and the link I will post below says as much.
I have already read that c) is true.
I am not as sure about e). There were several articles that stated this. However, when I have re-formatted then reloaded Vista Upgrade in the past, I used the "install twice" trick. I have never attempted to reload XP.
As to a), there were several articles written in July that said that some spokesman from Microsoft indicated that an upgrade from RC was possible with the Win 7 Upgrade version. However, the article linked below has the actual error screen that shows up when you try to do it. This link is supposed to show how to tweek a file on the Upgrad disk and change the registry in the RC install to allow an RC to Win 7 Upgrade install. Not sure if I want to try this but "what can I lose?" Instead of doing an upgrade as stated (and risk instability) I would probably make a bootable iso of the changed Upgrade files and do a clean install.