■Use one 500 GB drive for the OS + programs. Put the other 500 GB drive in a desk drawer.
■Use the 2 TB drive for data and games.
■Use the 1 TB drive to backup your important data for now.
At some point in the future:
■Buy a 500 GB SSD. Clone your 500 GB OS + program HDD to the SSD. Put the 500 GB HDD in the desk drawer.
■Eventually buy a RAID enclosure. Toss the 1TB + 2 500GB drives in there, set up as JBOD so they look like one 2 TB drive. Use it to make backups. You want your backup drive to be external and disconnected when not managing backups, so that a lightning strike or ransomware does not destroy your backup along with the original. https://www.newegg.com/RAID-Enclosure-Subsystems/SubCategory/ID-509
■If/when you upgrade to a larger HDD for data, you can toss the 2 TB drive into the RAID enclosure and continue using it for backups (since its capacity will now be 2 + 1 + 0.5 + 0.5 = 4 TB).
Putting the OS on one of the 500GB drives might help save potential headache down the road if you decide to upgrade your OS to an SSD for the simple reason that whatever you have on the OS drive now is going to be easier financially to get to fit on an SSD than things on your 1TB or 2TB drives, while it should allow you to just leave the larger drives alone when you go to switch over as well.