Discnumber filling

You can already get the discnumber with the function Convert>Filename-Tag:
Format string: Album Disc%discnumber%\%dummy%

For general requests on a discnumbering wizard see this thread.
/t/11387/1

What kind of filesystem are you using? Windows NTFS would not allow different folders where only the case varies. "1a" and "1A" would be treated as the same folders.