Hello, Dan E.
Well, I'd recommend using only the firewall component of Comodo, since its antivirus might conflict with Avast's. Not only performance wise (where luckily you haven't encountered any problem), but also protection wise.
Secondly, I like the fact that you keep a lot of backups. Great move!
Now, consider adding Adblock to IE (or installing the desktop version of Adguard) to block some annoying ads and speed up your browsing.
Finally, you mentioned that you just finished cleaning up your PC from infections, but since you have a basic computer knowledge, are you sure you can handle Sandboxie? Read some guides (including ones here, on MT) to have a more complete idea of how it works.
Thanks for sharing.