Planning a trip for early Sept and thinking of going to some new places. We are pretty set on starting in Iceland for 4/5 days. After that it gets a little more confusing. We are interested in Sweden, Denmark, Norway and The Netherlands, we can't do all of them so need to come up with a plan. Probably looking at 10 additional days aside from the Iceland time. Look forward to hearing ideas/suggestions......Thanks in advance

Browsing some of the guidebooks in your local library or bookstore would be a good idea!

FWIW, I think its reasonable to plan on about 5 days for a first visit to Stockholm (to include a day trip on the archipelago, but not counting elsewhere in Sweden), 3 or 4 days for a first visit to Copenhagen (to include a day trip to Roskilde, but not counting anywhere else in Denmark), the Netherlands could take weeks....

What are your thoughts if we were to do Denmark and the Netherlands instead? I guess I'm wondering which two would be better. We haven't been to any of them.

It really depends on your interests! None of us can say what YOU will find better than anything else. And there are no bad choices in the set -- just difficult ones. ;-) Again, consulting some good guidebooks should prove very useful. To start, maybe try some of the ones with high quality photos, such as the National Geographic or DK Eyewitness. Good luck!

Just saying that The Netherlands isn't a Scandinavian country.

Neither is Iceland.
Cities or scenery?
For scenery consider Norway - https://www.visitnorway.com/?lang=uk