Teaching your dog not to Bite
Take him by the jowl on the top pinch to the bottom and shut the mouth. Say "no, no, no, no bite" repeat it 2x
Sit and Leash Training
I do not use food to entice good behavior. I have them on a leash without any lead what so ever. I use a harness not a collar. (my preference-neck jerking is not good for a dog)
Separation Anxiety
First off separation anxiety doesn't last forever if you deal with it properly. Always remember trust takes time. I use soothing music or a noise maker to keep a consistent noise that brings ease to the spirit.