I think I'm going to settle on:

* Shen-Hao 4x5 camera (folding variant) + 6x12 back.
* Nikon 65/4 Nikkor-SW (angle of view: ~80 degrees horizontal, ~43 degrees vertical)

I plan to expand the system later with 135 and 250 lenses...

Thank you all for suggestions!

Regards,
Loris.