Viki, first - congratulations on the growth of your practice!
While I haven't had the experience of introducing a new team to my clientele I do have the usual annoucements regarding rate changes, vacation days, etc. and I have always found that simple and straightforward is best and I try to give ample notice, with a follow up right before the impending change or event takes place.
It sounds like you have your bases covered and are just about ready to inform your clients, I'm sure they'll be very happy to know you've created a practice that can service their growing needs from many different angles.
Again, congrats!