If you grew them, know they have not been doused with pesticides, and are unconcerned about what has been climbing around on them, you don't need to wash them. Otherwise, do wash them, gently, and do it before you freeze them. Thawed berries tend to weep and are very fragile, and you wouldn't want to wash away their flavor when you scour the pesticides off them.
The best way to freeze blueberries is in a single layer on a baking sheet. Dry them as well as you can first without bruising them by laying them on a layer of paper towels and covering them with more paper towels. Place them lovingly, and without crowding them, on the baking sheet, pop it in the freezer, and wait. Once frozen, pack the berries into appropriate storage containers and return them to the freezer.
There are certainly some applications where you don't need to thaw the berries before use - blueberry muffins, for example, where they will thaw and cook in the muffins. Where they will be used as a topping or garnish, however, it is nice to thaw them first so that you don't wind up biting a crystallized berry.