Well if you're going to get into the expense of 8x10 holders then you may as well buy and old 8x10 field camera, like a poco or korona or such.
I would suggest making some nice, low tech wooden boxes and just make a door to slip some film in and clip it into place. You don't need anything fancy like a holder for pinhole- the film can be quite curved and still give a nice result. In fact, a paint can with a hole in it might be just the thing. If you ant to get fancy you could come up with some sort of bellows or sliding mechanism to optimize the effective focal length.
For film size, let me suggest 5x8- you get two sheets per 8x10 and the print size is quite nice. You might try some ortho film, that should be fine and you can easily develop it by inspection, which is handy with pinhole.
It's pinhole- be inventive and quirky and you'll get something nice!