(1) & (2) Slide to B&W film negative at the final image size. Pt/PD is a contact printing, so the negative has to be the size of the finished print. This issue would be that color film would not expose with true tonal values on regular film. (3) No, you can start with the original slide and then enlarge to the B&W negative for Pt/Pd printing.(posted 8087 days ago)This is a case where digital would make the conversion from a color positive to a B&W negative (somewhat) easier. Dan Burkholder's Book on Digital negatives for Contact Printing covers the "how to" of this process.