In the past with a new pc/laptop I have always created a partition D for all my data files to shield them from the Internet.
Is this necessary with Windows 10@
If so how should I do this?
I have not taken to this OneDrive.
I like to have all my data in one place with its sub folders as I have in the past.
Keeping your data on a separate disk/partition (as you are doing) is highly recommended.
If you create an image of your Operating System on C:, you are keeping the image to a reasonable size as you are not imaging your data - just your OS.
That is not the way things work - connected data is always vulnerable.
Backup your data on D: separately and don't leave the backup media connected.
Ransomware can encrypt data on all connected drives (Including network drives)