Hi DNA,
I am just back from N. Sulawesi. I spent 17 days there and had a great time. The diving is easy and the water was warm. I was lucky to see lots of pelagic fish due to a cold water upwelling (including a good 10 minute snorkel with a pod of dolphins). The small stuff is also there in good quantities and the landscapes are impressive as well. You won't regret going unless you have a hick-up along the way. The people are also friendly and it's very safe. 50/50 Christian and Muslim. Good people there.
I stayed at Santika and dived with Thalassa. September is a transition month so the weather should be good and your chances of seeing alot of amazing reef life is good as well as avoiding any crowds unless you happen to hit it during a Japanese holiday week. Don't worry though there are 50 some dive sites there and the boats avoid each other. I went last year in August as well and stayed part of the time at the Lembeh Resort. The diving was good but I found the resort to be a bit isolated for my taste. But then again i was a single. If you're a photogrpaher and going with a significant other or at least another, you should be good. KBR has remodelled and was looking good when I was there this year and I heard they added a pool. Not sure if thats true but it's also an option. I have couple of trip reports if you are interested. Just drop me a mail.
Deano2