Agreed. My philosophy has been to aim for the 12 month range to begin...they grow with you, you won't have to recruit/interview/transition for 3+ years...also they'll perhaps have siblings eventually to grow your business even more.
You will find that you will develop curriculum for each stage and schedule your day accordingly. My babies are more than happy with their tub of toys/activities or even sitting in learning with the older ones and vise versa.