can you follow symbolic links/shortcut instead of strictly directory structure?

That's exactly what mp3tofid does. You can create hard links to tunes and
soft links to tunes and directories, and mp3tofid will follow them
intelligently (better to use soft links than hard links, though).

But you need a native unix filesystem to create hard links or symbolic links.

cygwin can emulate symbolic links on windows nicely using windows shortcuts, but has a (so far)
unusable inode emulation.

i'm not sure if i delete a song, will the next song added use the same fid.

That's up to the filesystem. Will it reuse the inode number, than the fid number
will be reused too. But that's really not a problem for mp3tofid or rsync.
The new tune might inherit the playcount of a deleted tune on the player,
but that happens with emplode too.

are you saying that if i had 2 files.. with fids on the extreme sides of the range.. it will maximise the database file?

Yes, every nonexisting fid number in between takes one byte.

Pim