I think I'm going to try and reproduce the bag in this picture. Looks like the bottom of the bag is pretty close to the length of the forearm. Height and opening width appear to be roughly the same measurement, which I'm going to call "long enough to create a pleasing shape to the bag." Basically, my first pilgrim's bag is just gonna be me totally wingin' it. This will also be the first actual project on which I've used our fancy industrial sewing machine.