I'd say do your best to acquire a lot of strange diverse skills. You may be a tech genius who discovers some brilliant insight that others have not, but you will potentially need executive leadership to steer the ship while you are CTO. Being an effective generalist means knowing a lot of different things and how all your teams will work together. So something may not be your direct interest (like marketing perhaps), but you damn sure want to at least know the basics of it so you can lead them.