Hello islandwaters and welcome to cruise-chat;
I think you will be completely happy with cabin L251; the overhang from the deck above will give you some protection from Alaskan drizzle, and you will have no noise or privacy issues. You are under the beauty salon which is not noisy at all and the walkway is used only for--walking. And the overhang is wide enough that nobody will be looking down into your balcony.
You are really in an ideal location; you have easy access to the pool areas, Horizon Court Buffet, pizza, a bar and The Grill. But you wil not have a noise problem as you are far enough forward--although I've never heard of any problems, even for the cabins right next to the Lido.
If you've done some reading in the Princess Forum, you know that Princess is my favorite cruise line and Sapphire Princess is my favorite Princess ship.
I know you will have a wonderful cruise and if I can be of further assistance, please just ask.