Yet where is God in all this? With all these devils, demons and extra-dimensional ne´r-do-wellers about - which He would have to have created - it would seem to make the universe a rather crowded and unruly place. It seems to me that having made Man in His image there´s plenty of depravity to deal with without invoking all sorts of bogeymen, which, by the way, there isn´t a shred of physical evidence to support at all.
That's an odd statement.
An infinite God could live in a realm of infinite universes or in an infinite universe (or both for that matter).
And because you (as a human being) do not see evidence of all that God has created you presume it doesn't exist?
The Bible tells us of angels, both holy and fallen. And the backstories to the Bible including the Pseudepigrapha (Enoch specifically, which part of the Essense's Sacred texts) and a massive amount of ancient Hebrew literature all speak of fallen angels and their role in the Fall of Man.