So, to confirm what I'm hearing:

Regarding disk drive building and storage:
Your guess is that a single 512GB CF card would be easier on RAM than, say, two 256GB CF cards, but that no one has reported trying a disk that big yet. And also, anyone attempting it should wait for a new version of your bigdisk builder.

Regarding song database size:
In the past we had determined that the player software could handle a database of somewhere between 10,000 and 20,000 songs, depending on how much data existed in the songs' tags.

Does that sound right?