Also, you won't need antivirus, but if you feel you must have one, ClamXav is the recommended one. To block nasty popup ads and malware in Safari, AdBlock+ and/or Ghostery will work well, and if you get the nasty popups, AdwareMedic should clean it up.
Also, use Time Machine for backups, but also consider either Carbon Copy Cloner or SuperDuper! to do backups that are bootable. If you want to run TimeMachine less than every hour (the default), you can get TimeMachineEditor and set longer intervals.