Thanks for the advice about the NAS. Perhaps it's best to leave critical data and backups to a professional product.

As for the firewall, I had a Ubiquiti Security Gateway for a while and it worked great. Not sure how it compares to the UniFi Dream Machine, however. The only reason I made a custom firewall is because I wanted to try and learn a bit about firewalls and routing in general. And, since my own device has worked well for me so far, I haven't bothered to replace it.