I was there in September, which is the off season, but it was still relatively busy. In my experience my wife and I were able to buy tickets to attractions on site, with the exception of the Anne Frank House. Even in September the line for that is very long. Buy those tickets ahead of time, but canal tours and museums should be really easy to buy tickets for. We didn't go to the palace, so I can't speak to that, but we did mostly everything else.
You must do a canal tour, but make sure you get a smaller more private tour, those are significantly more fun than a big boat with lots of people. Also get out into the countryside if you can, towns that are even 20 minutes outside of Amsterdam are very quaint and peaceful.
Hope you have a great time! Amsterdam is one of my favorite cities in all of Europe!