Okay, I have done a cruise. My folks did the Alaska cruise. And I've been to Alaska in May and June to many of the areas you're talking about (but not by cruise). Here are my tips:
1. Yes, rent and bring the 500mm. Bears will be out towards the end of May and June foraging for food after their hibernation. Eagles will blow you away (especially in areas where there is scavenging to be had). You'll see them often, up close, and in great numbers if you're lucky.
2. Juneau is touristy and a cruise port-of-call...lots of fake saloons and similar cheesy establishments, very crowded when a cruise ship is in port. You can get some dramatic shots of the surroundings mountains at Juneau (see below) without leaving the town. Same with eagles.
3. White nights: be prepared to have blackout glasses/mask or sleep about 2-3 hours a night and catch-up at a later time. Lovely sights. Almost anytime you can shoot with ambient light.
4. You probably won't be able to get any aurora borealis shots but still prepare "just in case".
5. Usually the glacier visit is to the Mendenhall glacier. Worth doing.
The first two shots below are shot from the city streets of Juneau in mid-May. The third shot is at 11:30pm in Fairbanks. The colorful sunset shot labeled "Fairbanks Sunset-3" is actually sunset in Anchorage (I know the photo says Fairbanks--I was sleep deprived when I did that post-processing). From what I've been told, you'll often be able to shoot whales or orcas from the deck of the cruise ship. Salmon spawning is late July so you'll probably miss that. Do Denali if you get a chance. Also, given some of what you like to shoot, if you plan ahead, you can find models in Alaska willing to pose for you.
As for cruise tips...I don't care for 'em, some people love them. Prepare to tip when you leave (so include that in your costs). You'll spend a lot of time getting on and off the cruise ship. You'll eat a ton. and then you'll eat some more. Some people go on cruise ships and focus on the food, the casino on the boat, the movies, etc.....I think that's a waste. You're going to be in fricking Alaska! Be the first person off the boat (which will likely mean queuing up) and the last person back on. Look to venture out of the tourist zones (like in Juneau or Anchorage). Get up early and stay up late in hopes of shooting sunrises and the northern lights or catching whales and orcas cavorting near by. The advice on layering (especially for this cruise) is accurate...on the water in the morning it will be cold. Check to see if you are expected to dress up for a meal--some cruises have that expectation (and you need to pack a tux or suit or something other than fleece and a Hawaiian shirt). As a photographer, they'll open up the midnight buffet 15 early for people to go take pictures...it's worth doing. And you will kick yourself for years if you don't bring gear good enough to shoot this opportunity. Maybe not a full duffle bag of stuff...but a tripod, a big lens for wildlife, a bunch of SD cards, batteries, definitely microfibre cloths (I was in Juneau in rainy season).
) That goes for aftershave's, etc as well. A nice odorless deodorant is also good. If they smell you not some pretty scent that is good, they will generally avoid encounters with humans if possible. July is mating season so beware. 
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