I highly recommend BitLocker on all drives, Windows will not only accumulate a significant amount of data over time that can be used to identify and break into your devices/drives/accounts, but it also caches file data locally, even if it is stored on encrypted drives; to be absolutely clear: data stored on any drive will leak onto the C: drive
Also, before you enable BitLocker I recommend that you configure the "Require additional authentication at startup" local group policy setting first: