To my mind, M3 (Pests. Diseases and Poisoning) is the other low-hanging-fruit after taking the Basic.
However, if you are a honey-show exhibitor, a botanist, a lawyer or a wax chandler, you might find M2 to be particularly accessible.
At a recent class, a very well qualified beek was suggesting that M5 (Anatomy etc) should be taken early - so as to provide a knowledge of the internal workings of the bee as an underpinning for subsequent learning about the external symptoms and behaviours (and thus beekeeper actions) for individual bees and colonies. Its just a bit daunting for the non-biologist!