Your needs in a service dog will be unique. No other person will require exactly what you need your dog to do for you.
So it makes total sense to train your own service dog and get exactly what you need.
But no matter what else you train your dog to do, bite inhibition is crucial. For any dog, pet or service. The joy goes right out the window when a puppy or adult dog bites someone.
See this quick video showing our trainer Robin teaching Sable how to resist the urge to bite hands - I've been using this ever since to teach her all kinds of other things too, like to watch me, sit, down and even come.
Lots of skills start out as fun games, like retrieving things. Balls, frisbees or just a stick can be the basis of learning how to go and get whatever the trainer wants.
Politeness, and giving up the object into hands or onto the lap of the trainer are a work in progress.