Welcome back to the forum. There are two possible answers to your problem.
The first is the easiest. Simply exclude the Previews folder from your backup schema. This is the approach that I take and I think most people do as well. What backup software do you use? You can use Crashplan to accomplish this. It is one of the backup apps that I use. It also works on Windows. I'm not that familiar with the backup app that ships with Win10 but it should be as customizable as Crashplan.
The second answer addresses your question directly. You can substitute a symbolic link to the Previews folder and then the Previews folder can be anywhere in your system as long as the name of the symbolic link is the same as the previews folder and the link resides in the folder alongside your catalog where LR will create a preview folder.
You can use the same options for the Smart Previews folder too. However, unless you are sync'ing with Lightroom Mobile or going portable and leaving your master image files on a EHD at home, you don't need the Smart Previews folder at all.
If you do actually use the smart Previews folder for one or both of these two reasons, you do not need to create a Smart Preview for every file on import. For LR Mobile you only need smart Previews for the images in the collections that get sync'd with the cloud. Also for the portable LR situation, you probably do not need every images accessible when you travel. Before the trip, you can decide which images that are in your master catalog that you actually plane to access during the trip and create Smart Previews for just those.