Well Joe that's quite a daunting task......pretty cool project though.
So it sounds like the documents/blue prints, etc will be called upon for future use, and they will probably be adding more as time goes on. Not sure what your budget looks like but when tasked with a similar project we used this company
www.edms.org (EDMS) there are also other companies out there such as Captaris, Ademero, etc. Do a google search for electronic document management.
Essentially a product like EDMS allows for organization, security, rapid retrieval, web based access and scalability.
"Some are 500 gigs each!"
WTF? 1/2 terabyte? You better buy a lot of DVD's (I think the largest DVD is 8.54GB), let me know which make so I can buy stock in it
As far as protecting the data on the disk I have personally never done this but there are tons of software options out there. You could either "protect" the disk or have the images protected with a water mark. If you never plan on having members copy from the disk then protecting the entire disk may be the way to go.