If you plan to shoot handheld, there is a grip/bracket for the Rolleiflex SL66, which provides for a more stable shooting platform. The SL66 is a sizable camera.
Some accessories from the SLX can used with the SL66, such as the compendium lens shade and even the 45-degree angle prism.
I haven't used a Hasselblad, so I can't provide any comments on it.
The Zeiss lenses for the SL66 are excellent. The early ones are single coated, I believe, so a lens shade is a wise accessory ... and in fact is always a wise accessory to own.