Where to start?

So we've got this amazingly wonderful horse at our barn
With great bloodlines and potential
Nobody ever took the time to do anything more than saddle break him..
So this wonderful horse is sitting doing nothing...
Abd I decided enough is enough and took on the challenge
And it was so perfect we were progressing
From only being rideable for 15 minutes to an hour and 15 minutes
He went from walking circles to walk trot canter and even a few "jumps"
If that's what you want to call them...
And then tragedy struck
He shattered his hind leg...
It's been almost 6 months since it happened and were excited
He's never shown any signs of pain
He's never limped
Even right after it happened and they performed surgery
He hopped right up and went walking away perfectly
Crazy?
So 6 months later after being confined to a stall
Were starting to inch our way back...
We can take him out into the ring for a little while
But that's about it so far...
So i've noticed a few things
The other day when I went in to do some grooming
He's picked up some extremely bad manners
He paws at the ground (dramaticly I might add)
He tosses his head constantly
And whenever I walk away he sends ear piercing screams throught the barn
I'm curious does anyone have tips to cure his habits
And does anyone have any ideas on where to start to work him
(veryyy slowly) back into things???
Anything will be very much appreciated

This might be really bad advice, but at my camp when a horse would start pawing I would pick up a piece of gravel and throw it at the ground underneath the horse. Don't actually hit the horse, just the ground underneath.
It seemed to work excellently. The horse doesn't think anybody's throwing the rock, they just figure that every time they paw they get this weird thing happening under them. This method probably wouldn't work so well in a stall, but it'll work in an arena.
Another idea about pawing: Maybe he needs more turn out time? Is he gelded?
One of the horses (a gelding, gelded late I think) at my camp would paw continuously when he was nervous or if a mare was in heat. Basically with him I just tried to make sure to give him lots of attention since I was his love and I tried to give him things to entertain his mind, like letting him graze loose outside the pasture, etc..
I'm not sure what to do about those other things.

Good luck!

It could be frustration. Just start on basic things, relaxation and flexiblity.

He's in a stall all day long due to the injury?
That's most probably it. Try to ignore the behavior and it will probably disappear when he can go out in the pasture again. He's bored.
Make sure he has enough straw/hay to eat at all times.
Some bad manners just won't disappear once they've come tho, since the horse kinda get addicted to them. (like ''swallowing'' air)