I agree with your mentor, put another box between the brood box and box with honey. Im not in your area so I will lean towards your mentors advice as to which size box to place on them, here I would give them another deep w/ foundation frames and move up 2 frames of brood into the new box, placing the other 2 foundation frames below between brood frames. Nurse bees would move up to tend the brood and as it emerges the queen will usually move up and lay in those frames as they are drawing the others. Due to seasonal constraints, length of flow, etc your mentor may be correct in advising to put a medium in there between the deep and the honey. Go with his advice if no others from your area chime in here, and good luck, you've got a good start for them with a full super for winter stores.