Yes, the focal plane shutter seems to be working well. It took me a while to work out how to set it though. Essentially the slit width is set first and this is the difficult bit as it involves depressing the shutter cocking knob during winding until you feel it disengage. It can then be set into one of several notches which adjust the slit width. Once this is done you continue to wind until the shutter is cocked. There is a separate small knob at the base of the camera which adjusts the shutter tension. By combining the tension settings with a particular slit width, a number of speeds are available to the user.
The camera came with three single plate holders also marked Van Neck which were obviously made for the camera as they are a very nice snug fit. You could well be right about the film packs as both the focusing hood and the back are removable. Indeed the way the back attaches is very similar to the universal back seen on the Graphics and MPP cameras alhough it does not have the brackets to hold a roll film back. I think as long as any film holder will fit physically, then there is every chance that it will be held in place securely by the spring tension on the back. I would need to check this though.