All those spinning HDs, all the fans to exhaust the case heat, lots of noise - and just for 192kbps...wow, weird.
MP3Pro would be a very bad idea, imo. So would WMA8. When he's done he's going to have a huge collection of material, the primary value of which being the time taken to do it. To lock himself into a going nowhere standard like MP3Pro or a highly controlled one like WMA might really limit his options in the future as to what portables he could throw data on and play it back properly.
Though definately consider your mp3 encoder carefully. LAME's encoder would probably be best. Be a real shame to rip all this using some crap encoder. I'd even say go for variable bitrate for improved quality with the same file size rather than to save space, but even that can be problematic with a few portables.
I'm not sure that the motherboard/cpu chosen for the encoding should necessarily be the same one used for the eventual server either. Is this mp3 server he's building to be his only machine or will it (once encoding is done) be a light duty machine only used for playback and encoding new arrivals? The encoding machine needs to be massively fast just because of the amount of encode time you're talking about here, but the playback machine should be reliable and quiet above all else, or so I'd think.
Just because of the heat/noise considerations I'd lean towards using external/removable drives as the backups and leaving them in a closet (somewhere else). RAID is great, as long as you can stand the heat. And the noise. And as long as your computer never gets struck by ligtening, burnt up in a fire, dropped by movers or stolen. External drives stored offsight do much better then. So would DVD/tape backup of course, though current DVD would be a pain and tape limits where the data can be read. With two sets of working drives he could have one setup at his office and one at home and if a disk fails, restore it from the other machine. External firewire (or even USB2.0) drives would be great here, he could disconnect the ones not in use and have them quietly powered down off to the side with just the one in use going at any time, either on system A or B or both. And lock them up when the brother's kids are over and want to use the computer
--Mc