Don't forget to budget for the tips on the ship!! I don't know what Carnival "recommends" but you need to plan on a "per person" rate of approx $3.50 a day each for the room steward and your table steward. $3.00 for your assistant waiter and tips to the bar tender, etc.
I also agree with the balcony. We've been on an Alaskan cruise 3 times and only once in a balcony (cost restraints). The balcony really made the trip special. We spent most of our "at sea" time out on it. We had an inside cabin on our last cruise, but were right next to the deck and could actually lean out from our cabin door and check out the weather.
We really enjoyed the whale watching tour with Orca Tours (Capt Larry) in Juneau. We also took the ship sponsored Sea Otter Tour out of Sitka. They were both really great and comparing them is like apples to oranges. Different experiences totally...
Juneau (being the state capital) has lots to see by walking around. Until you know the time in port, it's hard to say what your options are. If you only have a short time, you can take one of the ship sponsored tours or walk into town and check out the museums and other exhibits.
I'd highly recommend that you get a copy of Mitchner's "Alaska" to read. It gives you a better insight to the wildlife, state and towns and a REAL big appreciation for those currently living there.
Do a search and check out previous messages on things to do in the ports. You're definitely going to love Alaska!