My mom usually makes a 12-pounder and that feeds 5 people with some leftovers (which is the best thing about turkey).
If you use the crockpot, the turkey breast will get "done" but it will not be crispy and you can't really baste it because you lose 20 minutes for every time you lift the lid.
You can add some chicken stock to the crock pot because the turkey breast does not release a lot of moisture.