I have no idea what's wrong with his neck. You said he injured it quite awhile back. Does not sound to me like Newcastle.
I have no idea if it's going to work because I don't know what's causing his eye issue. If it's bacterial and related to ONLY the eye, not some systemic respiratory illness, it might help.
I wouldn't do another surgery on this bird. Didn't sound to me like the vet knew all that much, but even if he did, bumblefoot can be hard to get rid of if he has some rough surface he's getting scrapes on his feet from. We usually do our own bumblefoot treatments as chicken owners here, like I showed you in the thread on bumblefoot surgery by our member "ruth".
I'm don't know if his environment is something contributing to his health issues or not. Does he get outside in fresh air at all? Does he get to dust-bathe to get rid of lice/mites? Has he been wormed at all in his life? He has to have somewhat of a normal life as a chicken to live a healthy life and I really am at a loss as to what his day to day routines are, what he's exposed to, etc. I wish I could help you more, but honestly, I really don't know what to tell you at this point.