I own an Anna Apple tree and I have to say it is a strong and vigorous grower.  The tree is partially self fertile and has really low chill hour requirements.  As I understand it the best pollinator for the Anna is the Dorsett Golden.  I have a hard time getting my Anna to enter dormancy in Winter.  I would love to hear your experience with that on your Anna apple tree especially if as I suspect you live in a higher lattitude than I do.  Regarding pruning....my Anna apple tree developed some black rot on the main leader the first year.  So I pruned the main trunk at about 2-3 feet above the grafting union.  After that the tree took off like a rocket and put in at least 5 feet of growth the following year.