Hello
This sounds exactly like what I went trough with Lilly. I too was so stressed about her not eating but really it was me causing the whole problem. As every time she went off her food I would add something different or swap flavours etc and she soon learnt that if she refused I would add a tasty topper or switch her food. I too was hand feeding her and she thought that was great!
In the end I got fed up of popping to the shops every other day to pick up something different when I new she was fine. She would still want treats and chicken breast etc
I would personally find something that you know suits him and he likes and stick with it. Put his food down for 15 minutes and what he doesn't eat after remove it and offer nothing until his next meal time. Then put it down again for 15 minutes etc. he won't starve himself.
At the time I settled for forthglade wet food with some Lillys kitchen kibble mixed in. She didn't eat every meal but eventually she learnt that I wasn't going to give her something else.
Now she loves her food! Although still has a day where she won't est a meal but as long as she is fine in her self I don't worry.
Good luck, hope you find something that suits soon