Ah. So you only have Kael maxed atm eh?
Okay. I wouldn't even be thinking about CB yet - let alone NM CB. Ditto for Doom Tower. Right now your focus needs to be getting five champs to 60, with max ascension and masteries, and, ideally, fully booked, so that you can farm Dragon 20.
The team I would build is:
Should I Use Any of The legendaries Or epics as Food? If Any Are Trash Or are They Good in their ways?
Do not use as food.
I assume you are f2p? Would not bother with kreela, I could be wrong but not a fan. Certainly would not book. Apothecary and warmaiden would be my next 2.