Hey there, Hi there, Ho there,
while I would recommend three or four days in the Tokyo Disney Resort I second the post above: try to explore a bit of the "real" Japan ... there is so much you could do.
If you are more or less restricted or have yourself restricted to Tokyo and the surrounding area there is still plenty to see and do. I would recommend the Lonely Planet (or Time Out) guidebooks for Tokyo. There were a great help during my visit a year ago. I loved wandering around Tokyo - so much to see.
Regarding Hakone: even if you don't want to spend two days for Hakone, I would recommend doing it as the "one day" Hakone Circuit. You get your ticket in Tokyo in the major train stations and then it is a one day roundtrip which takes you to the country side on train, cable car, boat, but and then back to Tokyo on the train. In between you get to see some breathtaking nature including a volcano and (if you are lucky) a postcard perfect view of Mount Fuji. The one day tour was one of my trip highlights. Depending on your interests you can emphasize different stops along the route, e.g. for an art museum or a walk around the volcano (recommended!). As I spend the rest of my time to explore Tokyo this was a really great change.
Oh and before I forget it: about those CDs ... Tokyo Disney has numerous releases so the problem might be choosing the best among the great, since nearly all of them are of interest. If you want to limit yourself, I would buy those CDs including material of shows / parades / events / attractions that appeal especially to you during the visits. Since the tracklistings on the back of the CDs are usually in English finding the right CDs is usually no problem.
If you want to splurge and want a great collection of past (not the current) music from Tokyo Disney go for the "Treasures of Fantasy" Disc set available in the music shop on Main Street of Tokyo Disneyland and at some other shops.
Otherwise you might be happy with the official album of both parks and selected show / parade / season CDs. Personally I would definitely recommend the soundtrack to BraviSEAmo! as a must get. Also take some time to browse through the "non-theme park" Disney CD release on sale in the music shop on Main Street, I found some great stuff there like "Disney on Classic" 2004 and 2005 with great symphonic recordings of the Disney material.
Yours
Dirk