Each build option is designed to have 2 at-will powers designed to work with it. As the game expanded to include more builds for each class, the number of powers expanded, and quite rapidly. As you level up, you can retrain 1 feat or 1 power or 1 skill. So, feel free to play around as you go. Figure out what works best for your character and build. Don't forget you can change the flavor text to be whatever you want. One Dragonborn wizard changed all his spells to be different special effects of his dragon breath. This doesn't change the key words or other mechanics--just provides a different description of the action(s).