It's much more than tidbits about Isis and Osiris being Dee's masters. And I'm not too sure about Josh being Marethyu. I'm not actually sure we'll ever found who or what Marethyu is. Sometimes secrets should always stay secret.
Also, Micheal Scott has offically named Machiavelli as the Warlock, which makes sense. Aten had to be convinced that he would be doing the right thing by betraying Danu Talis and it could be said that Billy the Kid was, more or less, just following Machiavelli.
And I have one question, how many people believe that Perenelle's aura is actually black? It was hinted at when she was helping Nicholas but I'm not so sure.