I think it takes a few cameras before you get it right. I have just started my fourth with numbers two and three not yet complete! You think of new ideas and solve problems as you go.
An example of this is the mechanism to rotate the front and back. For ages this was a mystery to me but after spending some time looking at pictures of cameras, mainly Wistas, I realise now how simple the mechanism is and have it drawn up to be included in the current camera.
It was also quite a help to see Ian's Wista a few months ago. If you know anyone near to you who owns a similar camera, try to have a look at it and get the owner to show you all of it's functions/movements.
My advice would be not to worry about getting it all perfect at first, just make a camera which you can use then learn from your mistakes and make a better one.
If you have managed to make a rectangular bellows then make a simple camera without a rotating back. Put a tripod thread on the bottom and on one side and rotate the whole camera instead of just the back. If you want light and compact for travelling, this might help.