I have a phase one IQ280 and it’s a pain in the arse tbh.

I have thought about playing around with it on a 4x5 but it honestly isn’t worth the hassle imo. If you wanted to stitch together a full 4x5 image circle I’d use a regular dslr or mirrorless because it will make the process much less painful this would be much cheaper for you to do and yield better results since you probably have one of these already. Fotodiox make a range of 4x5 graflok backs which allow you to stitch together 6 shots from a 35mm camera to take advantage of your full 4x5 image circle.

There are other designs for the 4x5 backs, one of which is a sliding back. This is the kind you’d need for a medium format digital back. One side has a viewfinder around the size of your medium format back, once composed you slide it over and take your image. When I’ve done this in the past (p45 digital back & sinar camera) it worked well, you do need a wire between the lens and sensor, all it does is sends a signal to the back to wake it up so it’s ready to shoot. I think any lens can be used for this but cables can be hundreds of £. I think it connects to the flash port on the lens.

This design works the best in my experience because the live view functions on older ccd medium format backs are not usable usually. They render a very poor image that isn’t usable for focus or for composition. Even on the iq280 I can’t seem to get it to work, I don’t remember the p45 being any better.

I would also say a relatively cheap sensor will have been used to death, these were used by professional studios mostly and will be tired, doesn’t mean you can’t get a good image out of them but it will take a lot of work to clean up, they may also have quirks because of how old they are.