When Kitty summoned Bartimaeus and mentioned Ptolemy, it seemed like an echo of Ptolemy possessed bart and excreted magic that bart was too weak to do. It seems weird, does anyone have any idea what that was about?

I don't think Ptolemy posessed Bart, Bart was just very affected by the use of Ptolemy's name. I think the magic was reacting uncontrolled to Bart's emotions. As for not having the power for it, he'd been in the OP for a few hours, enough for some of his energy to reform

No I think it is highly unlikely as Bartimaeus never mentions it and when he enters Nathaniel's body we is brand new to the concept. 

Djinni of books or Noah