<p>Tom, I have nothing substantial to add to the excellent advice given, except to say that this is one of the most difficult aspects of the process. You are not just gauging chances, your child is determining how many apps are "enough". The answer is not just a matter of statistics (if it was, this would be easy!), the answer also involves how much of a chance is the kid willing to take and how much your family can afford to pay. I think that you are on the money with your assessment. The caveat is don't fall into the trap of thinking that match equals admission - that is what safeties are for.
Personally, I thought of a match as where my child had a 50-50 chance, but of course that means she would get rejected from 2/4 matches. Often people don't really get the 50% failure rate.</p>