I have not been on the Statendam but have cruised Alaska multiple times and will be cruising Alaska again in May myself. May is considered one of the dryer months for Alaska but you can count on rain in Ketchikan because that is a rain forest area. Temps on average should be in the mid 50's to mid 60's but like mother nature tends to do it can be in the 40's or up into the 70's. This is the reason you bring layers to wear in Alaska especially in the begining of May.
For Alaska in May expect to see thousands of waterfalls due to snow melt. Expect to take more pictures than you have ever taken. Expect to see some extremely beautiful sites.
As far as tours go there are a wide range of tours and some can get very pricey.
In Ketchikan going on a tour to the Totem Parks can be interesting. A harbor tour I found to be more interesting than a land town tour. Kayaking out of Ketchikan is a lot of fun with some great things to see. There are also flight tours out of Ketchikan.
In Juneau whale watching is well worth trying. We personally use Capt Larry with Orca Enterprises instead of the ships tours. The Naturalists from the ships use him. A helicopter flight and landing on a Glacier is great here also. There are tours to Mendenhall Glacier at reasonable prices here. A raft ride down the river from Mendenhall Glacier can be fun if the river is flowing pretty good. There are a lot of gold mine tours here.
In Skagway you can take a tour back into the Yukon. The Whitepass Railway has some unbelievable views. Helicopter tours onto glaciers are good here. Panning for Gold tours are here. You can also take tours to Haines from Skagway, these are about a 45 minute boat ride to get to Haines.
I hope this helps you with some ideas. Flight tours and whale watches will be the most expensive. You can see most or all of these towns by just walking. Juneau will be the largest town but you can cover most the interesting parts of town by walking.
