What linux user accounts should be created prior to Drupal 7 install?
With your own user is enough.

If you want know how setup permissions check securing file permissions drupal community doc. It's referenced in this related issue.

In that specific case (setting up permissions for modules folder), it says the following:


  drwxr-x--- 32 greg-user   www-data    4096 2008-01-18 11:48 modules/


Now docs examples are for D8 but it works for D7 too.