- exFAT is an usual format, hence it’s not enabled by default in Raspbian (or PiMusicbox). I will see about adding it to the next release since it seems trivial to do so.
- FAT32 has a 4GB maximum file size limit and also a maximum partition size of 2TB. However, I don’t see why you can’t just have two 2TB partitions on a 4TB disk…
- NTFS is best if you are mostly using it with Windows (faster than FAT32 and no size limits). It is supported under Linux to varying degrees, reading is generally fine.
- ext3/4 etc are best if you are only using it with Linux.
Which format is best for you depends on what systems you want to use the drive with. If the drive is always going to sit inside a Linux NAS (Synology etc) then I’d personally go for ext4. But note that if you later wanted to connect the drive directly to your Windows PC it won’t be able to read it.
If you don’t have files larger than 4GB then there’s nothing much wrong with FAT32 since it works with everything. If you do have files greater than 4GB and you want to plug it into Windows then go with NTFS.
There’s lots more opinions and info elsewhere online so you might find better info elsewhere but the above should be roughly correct.