Often people see a roach back as a bad thing. It is not.. it is a strong conformation and preferable to a weak back that will sway with age. His back may make him a bit stiff, but he will be OK. It is a very short back and that is a good thing, tho he may forge at the trot, especially with those long toes. If he does you will need to see if doing rocker toes in front will help.
That throatlatch, in a Thoroughbred is DESIRABLE. It is wide and allows for better air flow.. and less chance of laryingeal collapse and roaring. It is not a fatty throatlatch at all.. just clean and wide. Just what you want.
His hocks could be a bit lower and he could have more muscle in his gaskins but he is in racing form and he will change with a difference in the work he must do and in the change in diet.
Give this boy a shot at letting down and then put a really solid foundation on him. Take your time because this is one that is worth it. This is a really really nice horse. If you don't like him, send him to me.