The best place to find answers to your questions is from a local breeder. I'm sure if you google your state and "dairy goat association" you can find your local club and breeders in your area.
All breeds produce wonderful milk and would be a great addition to your herd. However individuals vary greatly and some areas have better animals in some breeds than in others. For example, here in Minnesota we have some incredible Oberhalsi but some parts of the country don't have many at all and what they have aren't very good. The same goes in all breeds.
There are differences between breeds but there are more differences between individuals.
IMO it's best to start with an older doe, starting with a first freshener or a kid can mean a very steep learning curve. Ask about CL and CAE in the herd you are considering buying an animal from and always ask to taste the goat's milk before you buy. Some animals just have better tasting milk than others.
There are many good websites to learn about goats. hoeggerfarmyard.com/the-farmyard/the-dairy/dairy-goat/