You might be deadest on creating your pinhole 100%DIY but I bought laser drilled pinholes from and am very impressed. The kit came with about 10 of various sizes with a sheet for recommended focal lengths and times. I make my own crude pinhole cameras too and found outsourcing this step easier. Plus they do a better job then I could ever do.
I think someone else could help you better on attaching the film holder. My cameras are simple copy paper boxes and I attach my paper with a little bit of gaffers tape. Crude but it works.
Good luck!