Alex,
1. Since you have a P25+ with a Hasselbad H mount, you will need an H mount adaptor. There used to be a 4x5 graflok back adaptor years ago but mostly it has vanished, but there is still a good option for you. Kapture group has a "Live View" view camera adaptor for your camera and mount, as well as other things that might interest you.
2&3. Have no experience with electronic shutters, so can't help you there, but I am quite sure that there are no 'jumping' aperture in manual copal shutters or electronic ones either. My guess would be that you would have to disable/ close 'live view', close the lens and set the f-stop and trip the shutter to capture an image. the electronic shutter might make it easier, less physical, more precise and faster. Most large format lens in studios that use strobes, use 1/60, 1/125 and possibly 1/250 depending on strobes sync. They can always use slower settings for effects, like 1sec with the light off to get a candle flame.
I am not sure how well or far live view can take you, it almost sounds like you want live view on for hours or the duration of the shoot. I am not sure that it will work like that. If you read the review of the Phase IQ180 back by Mark D., he mentions that out doors you will need up to a 9-stop ND filter to prevent the chip from being "over-saturated", how it will work in a studio under modeling lights is uncertain. I have been using a Leaf 17wi back with a Live View dongle, in ugly B&W for about 5 years and have not bothered to use it for the past three years as I can do it better and faster with a ground glass and a focusing technique.
Two things to be concerned about is the image circle of the lens you choose and the camera to subject distance. Most of the new digital lens from 120mm down can have quite small image circles that will quickly impact tilts and swings. Even though you have a 4x5 camera, it is really not a 4x5 camera once a much smaller size digital back is attached. It becomes a 2.25x2.75" camera. So a product distance of 6 feet between the camera and the subject with a 120mm lens on 4x5 film, becomes something like 11-12 feet with a digital back and the same 120mm lens (to keep the same 6ft. distance with a digital back you would need to use a 65mm lens). You might actually prefer the longer distance.
Brian
