Check the port schedules when they come out. Sitka is always tendered.
Dress warmer, you'll have no control over the ship tempture, bring layers anyway- you definately need them in Alaska.
As for shore excursions, you need to do some homework first. Look over a shore excursion list and narrow down your interests and determine your budget. Then repost your priorities. There is no point in me raving about my favorites when they aren't for you.