With that figures, yes I agree it is pretty doable! I would guess that the library was much bigger! (My guess is that the image sizes are a bit bigger (even in average) since I see a lot of pictures easily hitting the 1M mark.
Still you have about 10 days to download everyting, which makes about 40G per day. Good luck, and If you need any help just say so.
(Ok.. just before submitting this I went to see my backup of BS folders and calculated the average of image sizes and it sticked under 150K.. I guess that maybe your calculations migth not be too far from the truth!)
(Maybe event pictures are larger than mocs..)