Sounds like you have the cutting plan figured out. The orientation of the grain is probably the only question, but it's not really critical. I wouldn't worry about it. As for the cutting length you should cut as long as you can and stagger the joints. I usually use butt joints. If it is possible you could turn your saw where the board is pointing out the door, window, or something like that, to get longer pieces. Regardless, you can build a fine boat using shorter pieces.