So, is Infinite somehow a special case with his power source, or do all magic users have a 'spirit of pandemonium' attached to them? If all magic users have an S.o.P. stuck to them, who's been doing the sticking? Because up until this point, all things pointed towards people with magic being born that way.
From the paladins comment, its at least all Pandemonium users who have a spirit attached to them. We dont know about other types yes.

And how special does this make Noah, since he apparently just randomly created a spirit of his own? Also, how inimical to humans are the various spirits, since Noah was warned against them?
Its in no way certain Ciel were created by Noah. Not after what we have seen with Infinity.