You can leave the NTFS format as is on the Win drive as Biab Mac will read it as it doesn't need write access to it.
This is a drive below that I used on the Mac, I renamed the Library to LibraryM then I create a symlink "Library" that points to LibraryM so it works on Win & Mac.
If you have 260gig free that will be enough to have m4a also allowing the drive to work on Win or Mac.

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