there are a couple pages on the web that detail how to make a simple bellows, i'll dig out a link for you later.

yes, you should measure from the film plane to the closest the bellows will close. that will give you the minimum focal length.

regarding syncinhg the shutter, I wouln't bother, just get a lens in a leaf shutter and when your ready to shoot just lock up the mirror and set the body to 'double exposure' mode.

most of the old 6x9 folder lenses will just about cover what you need with modest movements. I imagine any of the 135mm lenses on a 9x12 camera will be more than enough.