Plant a good pasture and keep it in good condition, that is #1.She should maintain good body condition just on pasture during the growing season with minimal grain.
A clean constant supply of water is very important. She's going to need a LOT of water to produce all that milk. That means investing in a water heater for your trough if you get winter weather below freezing.
Buy good quality hay for winter; alfalfa for when she's in milk and grass for when she's dry.
Have free choice mineral supplement, so her diet is balanced.
Find a good (local) large animal vet that is knowledgable, you never know when you might have an emergency.
Visit the "Keeping A Family Cow" forum online for more knowledge, they are really great over there too.