I'm overwhelmed with all these responses within one day. Thank you all!
My conclusions for now:
1) It's gonna be a simple concept with a fixed focus lens. For this I have to calculate the film-to-flange distance (depending on the lens of choice) and the hyperfocal distance (thank you Ian for the PM about these issues).
2) I'm not gonna use a helical focus mount for now (to reduce costs). Maybe in time if my concept works and I can get one 2nd hand & cheaper. I like Steve's solution by using an broken Olympus 50 mm lens to build his own helical focus device. If there is such a solution for my lens, I might try this as well after I have finished the camera. (See Steve's Building a 6x12 Wide Angle Panoramic camera)
3) I also thought of making 2 tight nested boxes, as suggested by John. But I'm gonna do this in an other project for a 8x10" wooden camera suited for 8x10" lenses and pinhole.
4) I'm gonna use Ilford Direct Positive Paper instead of film in this camera. I’ll also use B&W negative photo paper to make paper negatives for contact printing (gum printing or salt printing).
5) I have to choose a lens for this camera. I think I'm gonna use my “Schneider-Kreuznach Super-Angulon 1:8/121 #7481057" since it has a working shutter and it will be a 4x5" camera.
6) Maybe I even go for a second 5x7" size P&S camera since I have about 8 of these film holders lying around (without a camera). For this camera I can use my Voigtlander Braunschweig Heliar 1:4,5/21 cm lens. However, this Compound shutter fires at one speed only (needs SLA?). But first let me make the 4x5" P&S camera.
7) As a thank you to Ned: I'm gonna call this my "set for eternity" camera project. ;-)
Any thoughts about these conclusions?
Bert from Holland