If you are interested in DBs I may recommend you the getdpi-forums, there are plenty of people who can give you first-hand information on these. Regarding the cameras: I donīt think there are many differences apart the TTL-feature. If you want to use it, get it 503-series, if not a 500 or 501 series will suffice. You can use flash with these too, using a flash with dedicated sensor.