How hard does he bite? is he drawing blood, doing deep punctures?
Does he grab people as they turn away?
Is he grabbing you when you pet him or when you ignore him?
Did the trainer suggest a choke collar on this dog?
This sounds like a dog that is under the impression he is running your 'pack' and that all in it need to follow his rules. His fearfulness or uncertainty can go with the issue that he doesn't really feel confident that he is the best one to be the leader and it can stress him if he is stuck with that role.
The trainer you spoke with did have the basics for you on how to deal with him but I can give you some more and some places to research for help.
The rules for him need to change to do him the most good. From now on he doesn't get anything he wants unless he does something you want. If he wants his dinner he must sit or it is not given to him. If he wants to go out the door again he must sit for you first. Same for putting on the leash. You can vary what you ask him to do, down, sit, speak but you ask him to do something to get petted, to have a toy thrown etc. so that essentially is saying 'please'. Getting what he wants is a reward for him instead of a privilege. This puts you humans in the leader role over time and drops him out of it.
When company is going to be coming in then he gets put on a leash, or behind a baby gate, or in a crate so that he does not get to choose what their behavior is as he is under your control. You can also teach him to run to a 'place' to lie down and stay when people come in. I would not use a choke collar with him.
If you have a local basic obedience class you can attend that would be good for him and you. But you want a reward oriented class not a choke collar class.
If he barks at you to demand something turn your back and fold your arms and ignore him until he stops with the barking.
This site down the bottom shows reward type training using a clicker
http://www.clickertrainusa.com/clicker-training-videos.htm
You may find the videos on this page useful
http://www.veoh.com/collection/imotd
for ideas on training.
This site has picture diagrams to help you see what the dog's attitude is
http://www2.aspca.org/site/DocServer/CanineBody_Language.pdf?docID=6521
and this one talks about calming signals to use with the dog
http://www.diamondsintheruff.com/calmingsignals.html
You will want to get your family and daytime pet sitter in on the handling methods so the dog is getting consistant training from everyone.
The hardest thing will be changing how you react to him.
Putting yourself in the leader role and demoting him from it should eliminate the biting issues because he will not have the right to boss you around.
More info here
http://www.clickersolutions.com/articles/2001b/discourage.htm
http://www.clickersolutions.com/articles/2001c/stoppingnegative.htm
Hope this helps you!
An upright tail is confidence, wagging is arousal (not friendliness a low held tail wagging is submission). Arousal is excitement - I had a dog that would wag his tail and bite people. He wagged his tail because he always enjoyed biting people (we resolved that but it took time and training). A looser lower held tail wag is usually more tentative friendliness.
A very stiff slightly slow wag is a warning sign much like a cat's tail twitching.
If I saw your dog with tail up, barking and stiffly wagging I'd know he was full of himself and felt confident he could control the situation, if need be with his mouth.
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics