How do students decide how many programs to reach out to?

Keep in mind your outreach should honest and genuine. It is not a good idea to reach out to multiple programs to tell them that they are your number one choice because this is obviously not true. Programs do talk. 

Deciding whether or not outreach is necessary depends upon the circumstances for each applicant. Your specialty advisor can help you make an assessment about competitiveness. For example, if you have heard from your specialty advisor you have a competitive application, outreach may not be necessary.  The yield for outreach is often low, but it may be slightly helpful. Your specialty advisor can best advise you regarding the culture of your specific specialty.