This isn't in direct response to any specific question, but have you used iTunes? I have a large mp3 collection also, about 17,000 songs and 100 gigs. I have about 400 cds that I'm going to rip as well. I find that iTunes works very well for me.

As for album art, I just pull up Amazon or Tower Records, then drag the image from their site into the appropriate part of the itunes window.

If you've got your files tagged by genre, you might like iTunes, which allows you to select or search by genre, and many other fields.

Besides, WMP sucks.