re: Pyrmont - there's a published guest list for May/June 1746 and it does have Quantz, the Bendas, and Salimbeni on it, but no Barbarina. From this, it seems safe to say that she didn't arrive with Fritz, but since it only starts May 17, she might have arrived earlier, on her own?
Re: Danish kings and their favorites: Oettinger's History of the Danish Court