Can Cass predict what your character is thinking/planning/doing? Yes, though he's not prone to showing off anything, and he's good at keeping things rather compartmentalized as you do know.
If yes, what limitations do you have on this? See above.
Is there anything you'd rather she not be able to predict? None that I can think of.
Anything else? Probably a no on the hacking, since he's never done a post that's been able to be hacked.