First of all, a disclaimer: I'm no expert. One of the best places to get informed answers on digital uw photography is at digitaldiver.net. I used to shoot with my 4040 in a PT-010 housing and now shoot with a 5050 w/ a PT-015 housing. Backscatter is often a challenge, but if you are doing closeup macro or supermacro, where the distance between your subject and the lens is not so great, then this will reduce the likelihood of backscatter. You can always clean some of that up with photo editing software like Photoshop.
With the PT-015 housing there is no bulkhead strobe connection. The connection that lets the camera "communicate" with the strobe is a fiber optic cable. The flash is important depending on the environment you are shooting in. Obviously, if you are diving clear tropical waters and relatively shallow reefs, you can get some very nice shots with the in-camera flash. My personal experience is that it's nice to start out with just the camera and housing and dive with it for a while until you really learn the camera. Learn to use the camera in full manual mode. This will give you much more control over your shots. Then, later on, if you want to get more serious with your photography, get a single strobe...and then move on to dual strobes if you feel you need them.
