I use a 2TB external HDD and SecondCopy software. I used to back up changed files on every shut down, but on upgrading to Windows 10 that became unreliable for some reason, so not back up changed files at 1 and 2 pm each arvo. I backup as a simple copy BTW so I can copy individual files back if I stupidly delete something I shouldn't, or if I have to replace the PC. Easy and simple.
I only backup data files.
Also because astro data tends to take up such a lot of space, each year I burn my raw data to DVD and remove it from the HDD leaving just the finished images.
I also a SATA cloning dock that I bought to increased the size of my C: drive, and I had every intention of doing periodic system clones o symplify re installation of thr system and software, but as yet I haven't found the motivation to match the intention...
Al.