YAY ~ Thank you for saving him....
Now, he is 3 y/o old, so it's going to take a good amount of time to understand him and train him to your house, etc....Remember that the first 3 years of his life are pretty much a mystery, and I am sure it wasn't a very good 3 years. But thankfully he is going to have nothing but love and comfort from here on out.
1. What food are you currently feeding him?
I would suggest the Merrick Dog Food. I would get both dry and wet. Dry I would get Grandma's Pot Pie and the wet I would get Winglin' - This is a very good brand, the wet has actual veggies, and a whole cooked chicken wing (you have to smash up the bone though) - BUT I bet he would be in pure heaven with the wet and I would mix some of the dry into the wet.
Best of Luck - keep us posted