Based on only moderate light fall-off near the ends, I'd say your pinhole to film spacing is probably OK. Several of the images appear to show camera motion during exposure; a solid way to anchor it would be good. I actually have a tripod socket (a 1/4-20 threaded "T-nut") in my most recent one. As others have said, there appears to be some light leaks too.
I didn't dig through that other site enough to learn what film format the guy was using. Generally from what I have seen, the larger the film format, the sharper the image. But sharpness can also be very much affected by the quality of the pinhole, as well as the size. A perfectly round hole with a knife edge in very thin material produces the best result.
You certainly got some recognizable results, it was a good attempt.
not so sure about the film size, 35 has always worked fine for me.
but you're right about the rest, pinhole quality is probably most important.