It depends on how competitive you are and how much money you want to spend.
If you have mediocre GPA/MCAT, no research or few leadership/volunteer experiences, generic LORs only, or from a less known school, then you want to go for a wider net.
Generally aim about 30-40 schools if you are not competitive. Beyond that, you just can't complete that many secondaries in time with good quality. And too many schools to keep track.
Your net can be smaller (10-20) if you decide not to apply to any reach schools.
Your net can be smaller (10-20) if you think you are almost guaranteed at your state school.
Apply broadly and pay attention to statistics on each school in the AMCAS book and also statistics from your school (where people end up).
And yes, DO THIS ONCE! It will keep you sane.