Some of us here have cruised HAL a great deal and are very happy to help with whatever questions you may have.
We leave next week for two weeks (back-to-backs) on Maasdam for a Canada/New England Itinerary. We've sailed this ship and this route many times and can't wait to do it again.
We think HAL keeps getting better and better.
Your method of choosing when to cruise is actually more common than one would think.

We do a similar thing as we often do back-to-backs and want to choose dates we can have the same cabin for both weeks thereby not having to switch cabins at the end of the first cruise. Availability of the same cabin for two consecutive cruises is our deciding factor on date to cruise.