Welcome to YT - you've come to the right place to learn about yorkies.
Bless you for giving this guy a new home. Love, trust and consistency will be the most important things for him.
I am heartbroken to think someone would have treated him so.
I second the idea of crate training him, this will be easiest on you and on him. When he is out of the crate interacting with you, you might want to consider confining the activity to one room initially too - closing a door or using a baby gate. Get an idea if he is housebroken.
As far as his weight, this may be natural for him or he may be overweight. Hard to know without seeing his frame & seeing where he is carrying the weight.The weight can be brought under control if he is in fact overweight, by controlling how much he eats & feeding a human quality dog food.
I have a little experience with this, just wanting to take 2 pounds off a dog I adopted. But others on YT have helped dogs shed much more than that. Just remember it will take time. And keep in mind love does not = food.
Can't wait to learn more about him
yorkiesmiles &
Bubba &
Roxie