First of all I think the basic idea of quick development and delivery is fine and if you can keep it then great, do so (it is the gist of the Agile Movement).
Question is why you have problems now? Is the problem that you cannot deliver as fast because you have more clients to share your time? Is the problem that the new employees cannot produce new code fast enough?
My personal guess is that you've found that "talent doesn't scale" and that you now have too few experienced programmers to do what you did before for more clients.
EDIT: If so, you need to acknowledge this fact, as it is impossible to throw additional people at the problem to keep the scaling (Brooks's law). Your experienced people will need to mentor new apprentices, and that will take some time.
