Well done!

Gradually building up on the hacks sounds like a good plan. If every day you get him nearer to the barking dogs, one day you'll have gone past them!

If he's nervous of other horses, is there any possibility you could get him more used to coming into contact with others? If not, don't get stressed; as the two of you go out more and more your bond and mutual trust will grow, and he'll trust you that he can just hold himself still while a perceived threat goes by.
One technique I've learned this last year has been an absolute boon to me. 'Pressure and release' basically means ask for something, keep on asking, but as soon as the horse yields
at all, take off the pressure. Then ask again, and again, as soon as he yields
at all, take off the pressure. Gradually he will offer more and more and in time you will be doing the whole thing at one ask. I would use this technique to go a little closer to those dogs each day - he will soon learn that going on isn't scary, because as soon as he yields, you stop pushing. Each day push him just a little further than he volunteered to go.
I used this technique to teach Davy that a puddle wasn't scary - and the second day he voluntarily walked right up to it and straight into it! Without my asking at all!

The other thing that you may have to bear in mind with a careful, clever horse like Bob is -
you are supposed to be the leader. If you let him make decisions about when to cross the road, turn for home, etc, he will start to think that
he is the leader and
has to make all the decisions. He will feel much less anxious and be much happier once you make it clear that
you make the decisions and all he has to do is whatever you ask! (Maybe he can give a little input now and again.

)
I wouldn't worry a bit about him breaking into trot and canter - the important thing is he came back to trot and then walk when you asked. So long as you both know he'll change down when asked, neither of you have to be anxious about him doing the odd change up when something excites or bothers him.
It sounds as though Bob is a really lovely boy who is naturally obedient and careful of his rider. Hopefully you can go on giving confidence to each other as you do more and more together.