Bedlam, what is it that you actually want people's thoughts on?
Do you want to rehome him? Do you want to train him to do something specific? ARe you worried about him with your/other people's children?
My only observation so far is that I would never personally mess around with my dog's food while he/she is eating - another one of those weird "dominance" thangs. We put food down, dog eats, we go do other stuff. Dog finishes food, disappears into garden, belches loudly and contentedly, bowls washed up. No Crackers of Destiny here.
Sounds like you're doing everything right to me. The handfeeding/adding to bowl is a good idea. I don't personally go along with the "I must be able to take food from my dog" dominance piffle either (my dogs are always left in their room to eat in peace), but adding to bowls and teaching them that humans near food bowl = Very Good Thing is totally different, not to mention necessary.
The panicking/biting when something's dropped is an odd one, isn't it? Maybe practise dropping stuff and click/treating at the same time, like you are with the collar thing. WRT the collar - consider having a short house line on him for times when you have to move him, so you don't have to grab his collar.
Do you reckon he's been told off for growling before? Often, when dogs bite "without warning" they've given plenty of warnings in the past (stiffening, lip-lifting, escalating to growling) and been told off for it. They then learn that growling etc doesn't work, and move on to biting.