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#41
Rule of thumb size: 50 to 60 percent of the sum of the occupied space on whatever partitions are included in the image.
Your C is about 100?
Figure 50 to 60 for the image. You'd want to include ALL partitions on that drive, not just C.
Normally...I'd save it wherever you normally would save an important file....likely on your old 1 TB drive.....AND THEN back it up to the external. So you'd have 2 copies of the image file.
You could use differentials if you want, but there's no over-riding reason to do so. You can just make periodic full images....perhaps monthly. Keep as many as you like....typically 2 or 3.
You can make a full image in about 7 or 8 mouse clicks, accepting defaults.
Restoration is more complicated, but worry about that AFTER you make the image.