Spring is generally the best time for planting most trees and shrubs.  If you purchase potting apple trees, they can be planted at anytime during the season. It would be wise to get them planted very soon if you need to, so they have a chance to acclimatize to their new home before cold weather begins.  Read the following information on growing apples in MN in the following publication.  It lists the specific kinds of apples that will grow best in our area along with proper site selection , planting and maintenance.  Select the disease resistant varieties to eliminate having to spray the trees often.
http://www.extension.umn.edu/distribution/horticulture/M1157.html

There is a good chance that squirrels are culprits that are taking bites out of your tomatoes, but if you have deer problems, they will also eat tomatoes.  Woodchucks enjoy them too.  Fencing is the the best option for stopping the feeding.  There are also animal deterrents such as Repellex or Hinder  are helpful in keeping the animals out of the garden.  Read the label carefully before using.