So many sob stories that could have been avoided.
Back up the original system before doing anything "mission critical" like a W10 upgrade. http://www.macrium.com/reflectfree.aspx is free and used by many people on this forum. Just remember to test your rescue media usb/cd after you've created it. Boot off it and make sure you can access your backup(s) then abort the programme.
Where you back up your system is up to the individual. I prefer another partition, external hdd, or networked NAS rather than a USB flash drive which can be fragile. You can never have too many backups.
I agree with you 100%. I have been using Macrium Reflect for quite some time. IMHO, it is the best out there. I use two external HD's for backups.