Font: I'd love to use Avenir Next for the book cover, because that's what we use throughout the app.
Colors: The blues & greens I included earlier are also used throughout the app. I'm picturing a gradient with blues/greens for the background and white text, but I'm excited to see what you come up with!
In general, I want an aesthetic that works nicely with StridesApp.com and ConquerApathy.com, but will hopefully be bold (with colors, icons, etc) to catch someone's eye.
One idea I've had so far is to include a bunch of little icons representing habits (e.g. Weight, Exercise, Drink Water, Save Money, Budget, etc) spread out all over the cover, at varying opacity levels so they look like they're in the background and don't reduce legibility of the cover text. Don't feel limited by this, just one thought to get the creative juices flowing. :)