1/2 week dumaguete...
You may as well dive Apo Island while you're there. I would also stick to 3-4 dive sites with the idea that you'll leave or stay longer at any one of them if you really like the diving. I would prefer to have a more relaxed itinerary myself unless you want to come back later to hit the spots you really liked for longer stays. One month sounds great. I once did 3 weeks and 3 different dive sites and that was plenty (35 dives in all).