An easy way to cleanup those paint spatters on area's that you don't want that spatter texture and water based paint is dry, use denatured or rubbing alcohol. Use small amount at a time. Let set for 30 seconds and apply again and it will come off.
To cut in wall to ceiling use the edge of your putty knife at edge of wall and ceiling. it will leave a small mark and a thin indent to help you keep a straight and clean edge.