Sadly yes.
Macs do indeed need Antivirus. Not as badly as windows but it is STILL a necessity especially if you want to avoid accidentally infecting your friends that are running Windows.
I would take the same steps above with gatekeeper and the firewall.
but also add-on something like
http://www.clamxav.com/ (or you can get it from the app-store if you don't need or want drivesentry (actually a folder/file monitor that monitors said folder/files of your choice) and do regularly scans once in awhile.
And perhaps WOT (Web Of Trust) to help steer clear of infected sites in the first place so your browser doesn't become a vector.
And I honestly highly recommend it.
(Note: It's a browser extension, and it works in most major browsers from Mac, to Windows, to Linux).
I take the same safety procedures on Linux using ClamAV (with ClamTK GUI).
Although for linux it's only just to be sure I don't give my Windows partition or my family malware by mistake since there's almost no malware for it. (And the malware that does come out for linux doesn't get to live very long before the hole or "exploit" it used to come through is patched up).
Also although this page is dated 2013 it does provide helpful advice.
http://appducate.com/2013/05/should-a-mac-use-an-anti-virus-or-anti-malware-app/