The amount of non-locking carabiners you need all depends on the type of climbing you do, the length of your climb, and how often you use non-locking carabiners while you climb.
For instance, sport and trad climbers will need more non-locking carabiners for carrying gear, building draws, and attaching to protection. They could benefit from having ten or more non-locking carabiners, depending on how long the climb is. Boulderers may not use any carabiners at all during a climb.