You tell the tree you want to make use of his services...once the window opens up where you can choose to brew potions...ALL the recipes for brewing will be used up..... Same thing with the Enchanter. He is by the wishing well near the West Shrine Portal.
Yes sell books once youve read them....I believe all your quest books are marked not for sale when you try selling them

Friendship is like peeing on yourself: everyone can see it, but only you get the warm feeling that it brings.