Hi Roman,
Wanted to answer your question about the calibration of the digital back and body;
Starting with the H3 platform, the H3 body and digital magazine where calibrated together at the factory as the two connected with each other that is unique and unlike another body/magazine hardware combination.
The
single benefit from this calibration is real-time lens focus adjustment as the camera compensates for the current aperture and modifies the focus of the lens to place the imaging plane directly on the surface of the sensor (because the protective glass plate acts as another lens element that will diffract the light rays based on aperture of the lens.)
The take-away, is that you would be able to use the digital magazine on another H3 or H4 body, you just would not get the real-time focus adjustment b/c the calibration capability is missing.
Additionally, the H3D 22MP sensor is indeed slightly larger than the 31 & 40MP sensors, but a moot point in practical photographic application - the 31 records more data so when viewing the final image @ 100% zoom between the two sensors, the difference is negligible.
Buying used does not preclude you from taking advantage of future Hasselblad trade-in promotions; the value of the camera is preserved for you as a second or third owner just as well as if you were the first owner.
You can see the trade-in chart
hereGood success in your hunting!
John