I built my pinhole by cutting a Pabst can and sanding the surface as thinly as possible and using a needle to make a tiny prick. Then I scanned the pinhole on my scanner and measured it in photoshop so I could figure out the rest.
Just some thoughts. And for the record, it's actually almost too sharp. Kinda funny.
http://www.f295.org/Pinholeforum/forum/Blah.pl? you can find cameras that are better works of art than the photographs they are apt to produce. Engineering at its best is as much an art as anything. However, it's nice when pinhole cameras, like other engineering projects, are also functional and put to good use.
I played with pinhole photography for a couple of years and can only say that it really is a lot of fun. I never cease to be amazed that so simple a contraption, made with a reasonable amount of care, can produce such amazing results, and so cheaply!
I have a couple of ancient, slightly warped 11x14" film holders a friend gave me a few years ago. Some day they will be put back to use in a pinhole camera. Should be tons of fun!
I just came back from Arches National Park after exposing about 18 paper negatives in the 8x10 format. It was a blast, very satisfying photographically. Many of the OP's questions have already been answered, so I'll just add a few thoughts.
Film holders: 8x10 fits nicely inside 8x10 film holders without any trimming of the paper required. This is not true with the 4x5 format. Carrying, say, four 8x10 holders in a backpack can, however, add significant weight if you're out on a photo safari like I was. Which brings me to my next thought...
Box cameras: The camera I've used for my last two photo vacations is an 8x10 box, made from black foamcore board and gaffer's tape, that's fairly wide angle in view. It uses "viewing dots" on the sides and top, which form triangles whose vertices are adjacent to the pinhole and edges of the film plane, giving one a pretty accurate method of framing one's images.
The major features of this particular box camera are that there's a side-opening lid, giving access to the interior, and a storage area behind the film plane, where exposed and unexposed paper is kept. Prior to leaving for my trip, I grabbed a stack of paper (about 1/4" thick, maybe 40-50 sheets) and slipped them into the rear-most storage slot. Then, when out in the field, I insert the entire box into a changing bag (which I carry inside my backpack) and load one sheet into the film plane.
Thus, this box camera doesn't use sheet film holders, yet permits me to carry (theoretically) more than a hundred shots in one vacation, all inside the one box.
The film plane is a sheet of galvanized steel, painted flat black, that has had its edges folded over to make film rails, on three sides. Thus, the paper negatives slide in and out easily. Since RC paper tends to bend away from the emulsion, and thus the center of the negative can thus bulge outward, toward the pinhole, you can either use a small piece of double-sided tape to secure the paper from slipping out of the film rails, or use a modified bulldog binder clip along the free side (this is the method I used on my most recent trip, and it worked well). The problem with double-sided tape is that it can sometimes leave debris on the backside of the paper.
The working method is thus load the paper, compose and shoot, then reload paper. You have to find, between each shot, a place to sit (preferably in the shade) and reload. It does slow down your progress a bit (if you're hiking with others) but it also gives you time to rest, and to contemplate your surroundings while reloading.
The advantage of this box camera method over using film holders is that it's lighter than carrying film holders, and after the eighth shot, with film holders (assuming you were carrying four such holders) you'd have to return to the car to reload the holders, since they take up more room in the changing bag to reload than does the box camera (you're better off reloading holders with a changing tent), and are harder to reload than the box.
I should also mention that I received quite a few comments and questions about the camera while on my vacation, affording me the opportunity to be a pinhole evangelist of sorts. Whatever method you use - sheet film holders or a multi-shot box camera - these can be lots of fun.
Contrast: Regarding control of contrast, I think you end up with a faster Exposure Index if you use low-numbered graded paper rather than filtering multigrade paper. I've done experiments using Ilford MG-RC-IV paper and a yellow filter, and it requires an Exposure Index of below 5; whereas my grade 2 RC paper from Freestyle (their Arista brand) I rate at an EI of 12.
Exposure/Development: This is real important, to find the proper EI of your paper, and properly expose it. I tend to use a handheld meter, and meter the brightest part of the landscape that I want to retain detail and place it at +1 stop on the meter. Then I reference the exposure time for f/128 on the meter (the highest f-stop that the meter will indicate) and perform the necessary conversion to my camera's f-stop. What I've done in this case is calculate a "k" factor ahead of time, which I've affixed via a label on the back of the camera, which in the case of this particular camera (f/258)is "4x". Thus, if the time adjacent to f/128 on the meter is 15 seconds, then the actual exposure time is 60 seconds.
Note that when metering, I try not to get the sky in the meter's 30-degree angle of acceptance, because I'm not interested in exposing for the sky, but for detail in the landscape.
Also, if your landscape has lots of red-toned rocks and earth, you need to extend your exposure time further. I usually give an extra stop of exposure in this case.
I either pre- or post- flash my paper negatives, to improve shadow detail. When loading up the box with a huge stack of paper, it's more convenient to post-flash each sheet prior to development.
I use the same dilution of paper developer (Ilford's Universal paper developer) diluted 1+15, but also mixed with an older batch that's almost black. When this new batch gets used up, it becomes the old batch, etc. I also ensure that the temperature is around 68f, and develop by inspection until the landscape detail is adequate, rather than sticking to a particular development time. This is important. A slight drop in temperature can significantly increase the development time; you can also somewhat compensate for moderate under-exposure by extending the development time.
This was somewhat rambling, topic-wise, but hope there's something of value.
Atop Delicate Arch, 80 second exposure:
Joe is the master of the pinhole.