Hello Monica, and welcome to Cruise-Chat;
congratulations on your first cruise; you have picked a great itinerary, a great cruise line and a great ship. Island Princess is one of my favorites: I have spent 30 days on her in the last year-and-a-half.
I'm sure you will be very happy with C335; it is a great location; you are half-way between the forward and midship elevators and stairs, you have cabins above and below, no equipment nearby, and the Caribe Deck balconies are larger than the other standard balcony cabins.
Volumes have been written for the first-time cruiser; but let me just make a couple of suggestions: you are on a cruisetour so pack light; but also be prepared for any kind of weather--Alaska is unpredictable. But most importantly, relax and don't worry about a thing. Princess has been cruising Alaska longer than any other line, and they have it down cold (pun intended). You wil have a crew of hundreds whose only reason for being is to make sure you have marvelous vacation with no worries.
If you have any specific questions, I'm sure we can help you find the answers.