No way, I am doing nearly this exact same project...!
I decided on an 8 inch (203mm) focal length, and just made a wooden box to fit some Lisco 8x10 holders that I picked up for cheap on eBay. Of course, film holders aren't 8" by 10", so I just traced an outline on wood and cut it to actual size. I ordered my pinhole from Lenox Laser in MD. The camera is nearly done, but I want to add some elastic to add some pressure to the back of the camera and hold the film holder in place. I may add a shutter, though the darkslide will probably make a good shutter as well, given that I'm going to start with paper negatives.
I have not worked with paper negatives before, but I have heard that a yellow filter or a 00 filter will help control contrast, and pre-flashing might also help.