I realize you asked about polyurathane...but I'd like to suggest a lacquer finish using a sprayer like the Campbell Hausfield Easy Sprayer. We build cabinets and use lacquer. It produces a fine furniture finish with fewer coats and work in between. Drying time is reduced to a fraction poly requires. Plus you don't have to worry about brush strokes. The spray systems are affordable for individual use.
Just a suggestion from someone who likes to save time and effort.