1) If you're really new, the one you should really try to CC first is Bashira (if you're too old to have gotten her, then skip this step). After than Katie, Iris, Cloris, Leanne in that order.

2) The failed early CC Crave can be used as awakening fodder later on, so just keep him around until you need it. Don't use him for exp (it's not worth it), I wouldn't work on him any more either.

3) Most people try to 1* skip castle retake in order to grind on the missions after it, which is easier than castle retake, and more rewarding than the ones before it. Skipping doesn't take much work as long as you know what's coming. 3* clearing it can be done later when your team is up to speed (and CCed).