Brought My First iMac - Need Advise on Virus Protection and Backup Please

Luke, no virus protection. The same goes for cleaning apps and most other third party utilities. Keep OS X up to date and use common sense safe computing practices and you'll be fine. Watch where you click.

For backups Apple's Time Machine is best IMO. Get an external hard drive 2-3 times the size of your internal drive and let Time Machine do it's thing. The first backup can take a long time but subsequent backups happen hourly in the background. you won't even know it's happening. The late Pondini can be your guide to everything Time Machine http://pondini.org/TM/FAQ.html

1. OS X already includes everything it needs to protect itself from viruses and malware. If you want your Mac to work properly, install no additional products claiming subject knowledge superior to the company that built it and the operating system it runs. Read Effective defenses against malware and other threats.
2. Yes, and your Retina MBP has the ability to restore OS X from the Internet, if the Recovery Partition should become damaged or unusable. A Time Machine backup or the equivalent is always a good idea, in the event you choose to install some completely worthless "anti-virus" garbage that winds up making your Mac unusable. To learn how to use Time Machine read Mac Basics: Time Machine backs up your Mac - Apple Support.

User Tip: Most commonly used backup methods

Emergency backups you didn't know you had!

Yes, always have at least one backup as the recovery only takes care of the OS, not your files or other user installed apps. Use either Time Machine or do a bootable clone backup using CarbonCopyCloner or SuperDuper which will help you get up and going quickly if there is a problem. You can just boot into that clone, wipe your internal hard drive with it and clone everything back.

For virus protection, it is not required.

For backup, enable Time Machine to backup to an external disk drive. The disk drive must be formatted as HFS+.