Id definately go with a seperate arm day. That way you can focus solely on your arms once a week. This has been working really well for me. Also, my arms are over 15 (just under 18 cold) and Ive always done direct work. Just be sure to train arms on a day that doesnt interfere with your back or chest work. Sore triceps before a chest day is never good. Ive been training my arms on friday. Using this split:
Monday: Back and deadlifts
Tuesday: off
Wednesday: off
Thursday: Chest (flat bench only, about 11 sets)
Friday: Tri's and Bi's
Saturday: off
Sunday: Incline bench, delts, rear delts
Also I train abs for strength 3x a week. You can add legs in there also. I havent been training them at the moment. They interfere with my deadlifting. haha. Hope that helps