I did this under linux using cdparanoia and two plextor SCSI drives. As I recall, it would prompt for a new disc every 30 seconds. That was quick enough to keep you pretty busy shuffling discs. That really isn't a lot of downtime. That box... That box ripped!
The encoding to flac was done asynchronously - there is no reason to do that at the time of the rip. On a very fast CPU, that would be less of a concern. Discs were tagged via a local copy of the cddb database, so no network connection was required. Unknown discs had to be tagged manually. It'd be easy to script a vid cam capture of the disc materials to maintain momentum.
All that on a very low power machine - I think it was a 300 mhz celeron.
Unfortunately I tore that sweet box apart to donate to my folks as a music server. They never use it