I agree with the neutral safety switch most likely being a problem with your starting issue. On my 1920 with the shuttle shift it was the shuttle NSS that went bad. It isn't a big issue to replace them.
Your second issue sounds like a nightmare. I would definitely contact a New Holland mechanic and get his advice and start trying to locate the parts you may need before splitting the tractor. It may be a smarter choice to get rid of it if its going to be a huge hassle.
I know I could not bring myself to bail out on this tractor without knowing exactly what is wrong, so selling before splitting is not in the cards. I might try isolating the bad switch(s) this weekend.
Thanks,
Steve W.