Welcome to TGS! :wave:
If you are serious about wanting milk goats, I would tell you to buy Alpines or Saanens. Nigerian Dwarf Goats are wonderful pets and sometimes good milk goats, but the standard breeds have the milk.
Most Nigerians around here are bred for their blue eyes and pretty colors, not for milk production. They don't often give more than 2 cups of milk a day. Granted, Nigerians give sweeter, creamier milk, but I found my family also loved the good sweet milk from my standard does.
Last spring I had 2 standard does which gave 1.5 gallons of milk a day, and a sweet little ND who gave a quart a day. I spent about the same amount of time milking each goat, (getting each doe on the milkstand, feeding her, milking her, taking her back to the pen), but I was getting 6 times as much milk from the standard does.
Whether you decide on Nigerians or a larger breed, please take the time to find and spend the money on a well bred milker. You will not regret it later. In my experience, a good milk doe should produce about 10% of their body weight in milk a day.
Also, a registered goat's kids tend to sell better. For example, last spring I sold my unregistered doe's kid for $50, and my registered doe's kid for $800. (The unregistered kid was actually much nicer.)
Enjoy the ride!