I use this to calculate the pinhole design: http://www.pinhole.cz/en/pinholedesigner/ it also gives you a table with reciprocity failure for different films.
Anyway, you don't have to focus with a pinhole camera, so you don't have that problem. The pinhole hole must be very precise in dimension and shape, usually a drill and other common perforating tools will give uneven edges, resulting in a some way distorted or uneven lighting of the film, the "best" pinholes are made with a precise laser cutting machine, but it depends on what you want to obtain.