Still working on this project. The first PC is up and running, collecting backups for my desktop PC, web server, and arcade machines. The second PC needs new capacitors on the motherboard. I will place an order for those soon, as well as a desoldering bulb, so I can set up the second backup device.
More importantly, I'm changing the direction of this project a bit. While it's nice to have my own PCs for backups, I want the focus to be on the software itself that is used to create and administer the machines. The eventual goal is a modified FreeBSD distribution (like FreeNAS) and instructions for how to build more servers of these from scratch. This means making a FreeBSD package - which means making a FreeBSD port - which means getting the code to a usable alpha version and putting it on Sourceforge.
Right now it's possible to connect to the site (thttpd + Perl), view basic disk usage information, and see the list of configured accounts. I am working on an authentication page using session cookies now: login with username "admin" to create / delete / manage users and global settings, or log in with a specific account name and get access only to that account's files, which can be used to restore backups from there.