What specifically are you after? You asked a question about NUM_INITAGENTS then dismiss the answer. You are mentioning "idle" processes but do not give a definition as to what you define as idle. Any agent not currently performing work in the database is idle. To count those is meaningless because you are getting a snapshot and the number at that time does not take into account how long they have been doing nothing. You need to define what "idle" means, then simply count those over the threshold.
Andy