That's the same machine that I am building but I have already started looking in to building another machine because of the problems & limitations this sort of machine has.
The book uses 1/2" threaded bar so not sure why you were looking as low as 8mm especially over that sort of length. Pitch on 12mm is generally 1.76 is it not?? Could be wrong about that as it's a while since I looked.

What are you looking to do with the machine?? What materials are you looking to cut with it. New myself so all I know is what I have picked up in a short time here. Tar as stuff like electronics goes I have been told to try & buy stuff that I can migrate to another build when the time comes.