Hi Pam,
We went through (..and are still going through!) a similar situation where there are teachers who use Moodle and do not necessarily know how to use the gradebook. Therefore any graded items they create will show up to the student as potentially incorrect due to the default aggregation.
We did change the default aggregation to sum of grades, like you mention above. At least with this type of aggregation the students will see a running total of their "raw points" which would not necessarily be incorrect. You can set the default in >Site Administration >Grades >Grade Category Settings
AFAIK there is no default to hide the total, the teacher would have to do this manually.
One other option we considered would be to default the course setting "show gradebook to students" to be "no" and that way the teacher is (hopefully) forced to learn the basics of the gradebook before they use it!