My 2015 15" MBP just arrived! Before i get started with it, i have a few questions: 1. Should i download Sierra right away? Should i back up the existing software before i do? I've never backed computer software before (only iPhones and iPads) so I'm not quite sure how this process works or if this is one i should even do. 2. Do macs need antiv virus software? I just renewed Norton for my Windows machine and have a few more downloads available. Or is there some built in software that is sufficient? I have heard that anti-virus software slows Down the computer a bit. Any thoughts? 3. Are there other settings or tips i should know before getting my first mac ready to go? I haven't used mac since my college days with mac os 8 or 9, so i know I'll have a lot of catching up to do! 4. Any online guides/youtube channels/references that can help me get up to speed on proficiency with the mac? Thanks!