When establishing an apple orchard, one of the biggest steps is buying your trees. These resources may guide you to find the right trees and the right nursery and to understand the process of procuring trees.
This is where you can find research-based information from America's land-grant universities enabled by eXtension.org
All about understanding and choosing the right rootstock
Characteristics, descriptions, and how to choose the best to grow and eat
Buying and planting trees
Insects, diseases, wildlife and other challenges
Grafting, budding, tissue culture, and all about how rootstocks are developed