Also im aware that base is not the proper term in this case since the base is still 10, but I have not idea how you would call the switch to the bigger unit treshhold
Actually "base" is entirely the correct term in this case. The first group to write down a really systematic method for timekeeping were the Sumerians, and they used base-60 math. This worked really well with solar and lunar cycles, which were important for crop planting, and with astronomical studies (mapping the stars had major applications for both navigation and religion, so it was culturally significant). Empires that came after the Sumerians copied and expanded their system, so it eventually spread to everyone.
You SHOULD NOT do software RAID with hard drives in separate external USB enclosures.
There will be absolutely no practical benefit to this setup, and it will just create risk of transcription errors between the mirrored drives due to any kind of problems with the USB connections, plus traffic overhead as the drives constantly update their mirroring. You will kill your USB controller, and/or the IO boards in the enclosures. It will be needlessly slow and not very fault-tolerant.
If this hardware setup is really your best option, what you should do is use 1 of the drives as the active primary for the server, and push backups to the other drive (with a properly configured backup application, not RAID mirroring). That way each drive is fully independent from the other, and the backup drive is not dependent on anything else. This will give you the best possible redundancy with this hardware.