I would recommend also trying to visit some of the fjords if you have the time and money. If you are going to Svalbard/Longyearbyen I would also go to Barentsburg, Pyramiden (if it is possible this time at the year, and also "Isfjord Radio".

I had a really nice guide when I went to Svalbard, if you want you could send me a PM and I will give you his contact information.

Have a nice trip!