To answer my own question, there doesn’t seem to be any option to allow it to automatically power on and boot when power is applied which is unfortunate.
I can probably deal with it as long as standby/sleep can last a few days though. It does seem to wake up although I’m not 100% sure it’s actually entering sleep mode at the moment.
And it seems to run continously charging somewhat slowly off about 1A i.e. about 5W. It never seems to draw any more than about 1A.