The trick is to get the lighting correct.
A few things I'd look for for a high volume document copy setup would be a deicated copy stand (not a tripod) so that you can set and forget your camera, lights etc and just concentrate on the documents and on the archive data to go with the image.
Shooting with a camera tethered to a laptop (something like a Nikon D80 would let you do that with Camera Control Pro software) makes the whole process much more relaxed.
Assuming your documents are all within a reasonable range of sizes then I'd go for a fixed focal length lens set at its optimum aperture.
The 50mm lenses are pretty much ideal for copy work as they have excellent sharpness, good contrast and a very flat field and should focus close enough for anything you need.
Set up everything with a test document of similar size to the documents you will be recording, set a manual exposure, manual focus distance etc. and record all your settings. If you are going to store BW copy then you don't need to do any particualrly fine colour ballancing but for colour work setting a custom white ballance should be done for your lighting set-up and should be repeated regualrly as the lights age and hte colour quality of the light changes.
Actually copying the documents is a two person job. One person to handle and position the documents and another to operate the camera (remotely) and to make sure that all the file names, image meta-data and descriptions are accurate.
Don't forget to budget for a back-up of all the archived data, preferably off-site, as well