Sheep and chickens get along well together. The chickens help keep the parasites and fly down in the sheep and the sheep seem to enjoy the chickens' company.
Need to keep the henhouse apart from the sheep as the sheep rub on it and disturb the chooks.
Protecting the trees is the tricky part. Some sheep like to eat bark, especially if they don't have sufficient minerals. Also, some breeds are good at walking on their hind legs - so I would choose a modern breed that likes to stick close to the ground.
If you are getting locker lambs (sometimes called freezer lambs) where you buy some in the spring then slaughter them in fall/winter, then be sure to get at least two as sheep are flock animals and they don't do well alone.