@Tony > FAT32 refers to the filesystem of the drive itself. All hard drives can be formatted to a variety of filesystems (FAT32, NTFS and exFAT are common Windows filesystems, and HFS+ is typically used by Macintosh computers) - but only FAT32 can be read/written-to by both Mac and Windows computers, which is why it is recommended when migrating between operating systems. That should be your first step; format your 3TB drive to FAT32.
Next, follow the instructions to move all of your music to the external drive, and relocate your database there as well.
Unfortunately there is no easy way to have the databases from two drives loaded simultaneously, and synchronizing / merging the data is not a fun thing to do on a regular basis, so the idea of 1000 songs internally should be done as an export from your main database instead of trying to maintain them separately.