Update regarding backup deduplication: I've started using BorgBackup and so far it's going very well. I even copied the backup folder onto my offline test VM along with the .deb files for BorgBackup and its prerequisites, and after installing the .deb files I was able to successfully list the backup's files and extract a sample.

(The TV's new prosthetic brain has less storage space than I thought, so it doesn't look like I'll be able to keep it on there. I'll leave the backup on my main computer temporarily and ask for an external hard drive for birthday or Hanukkah or something.)