What you're talking about is Digital Asset Management. There's some great info out there from Peter Krogh.
There is no reason to export JPGs to keep and if you're printing, you'll want to export them as TIFFs anyway. The great thing about Lightroom is that it's PIEware. Here's the way I manage my images which are over ten-thousand for my personal catalog and roughly three to four thousand for my school/ professional catalog. I keep them all in the catalog unless I need a JPG or Tiff for some reason. I even print from within Lightroom unless I've worked the file up in Photoshop, then I print from there.
- I import my images from disk and convert them to DNG and I also save a backup as the original extension (NEF for me since I shoot a Nikon). These are imported into a folder entitled "Landing Zone."
- Once I verify that all of the images were properly imported from my card to my HDD (I use an external rugged LaCie) I move the images from "Landing Zone" to "Rate and Adjust."
- In "Rate and Adjust" I do just that. I give the ones I like stars (1-5) based on the image and add keywords to aid in retrieving images later on. I also do any color correction, cropping, etc in this folder.
- Once that is done and I'm happy with the image, I move them to a third folder, "Transfer Me." Here they are stored in "buckets" labeled DVDDNG_000X where "X" equals the sequential number of the DVD in use. Each "bucket" is only as large as an Archival DVD (I prefer Gold Verbatim) which is roughly 4.3GB. Once a bucket is full, I burn that folder to a DVD, label it and store it. Archival grade DVDs are necessary for that.
- Once the DVD is burned, I move that file out of "Transfer Me" and into "Image Vault." The images will live the rest of their life here. Also, once the images have been burned to Disk, you can delete the folder containing the copies of the original images (NEFs for me).