Between CJ and Infiltration, whichever has the highest defense bonus is the one you'll be seeing active. They don't stack (to my knowledge, but I'm not on beta to provide evidence to support this) when you enter combat and lose Infiltration's bonus, CJ def bonus will become active until re-entering non combat status.
If you're planning on using Infiltration as a travel power alone I'd recommend 3 slots (see my yellow highlighted slotting in the above post). If you're going to use it as a travel power and boost its out of combat defense or run IO bonuses, I'd say 5, with 3 as mentioned before and add a LoTG or two.