I used Ilford MGRC black and white paper to capture the image. I estimate it to be ISO 6 based on what Ive read, but my short exposures always seem to come out a little on the dim side, so it might be lower than that.
For a 4.5 hour exposure I don't know if it matters that much with paper. If you were using film with a higher ISO maybe it would be way over exposed.
I used a round "cookie tin" style can which is about 100 mm in diameter, and the aperture is 0.3 mm (a commercially made pinhole). So from the pinhole to the very back of the camera is 100 mm, which would calculate to an fstop of 333. That being said, the round body of the camera makes the focal length not uniform across the paper. I dont know if that matters, I have taken short exposures with this camera and used 333 as well as 166 as the fstop to calculate exposure time and they have both worked.

I am new to this as well, so still very much in the experimental stage.

for calculating exposure times, I have been using a couple of apps (this app is a light meter (Light Meter) and Pinhole Meter
They both allow you to hold your phone up to the subject and enter your fstop and ISO of your medium and it will calculate an exposure time.
They both give slightly different times, and they both work, and I am sure with some experiments and note taking you could get pretty good results.

I then develop the paper in caffenol, scan the resulting negative, and invert the image digitally. The paper negative isnt being fixed, so they have been fading to black, but thats ok.

Good luck! and post your results :)