Partition the drive, leave the op system on a partition with 20% spare space.
load your programs to another partition and data to a third.
using the USB2 external as a working drive is too slow for photo / video work.
Image the op system partition - keeping this partition small +20% makes for quicker imaging and replacing if windows has a problem.
back up your data partition regularly to the external drive
Use something like CCleaner to keep the rubbish files down I clear about 400Mb daily that soon mounts up