I have been using exfat since it has support for big ISOs and is compatible with Linux.
The ST400 does NOT support ext4, but I didn’t care much: I wanted a partition scheme that was accessible from both Windows and Linux.
I don’t recall ever having to change the firmware for that, nor for NTFS which I have used the very first time when testing it out.
For my use case, I am using a cheap 120G ssd on which I only keep ISOs, so I never found myself needing multiple partitions…
Edit: The documentation does say that it supports multiple partitions, but again, I never tested that out, so YMMV…
Hope this helps.
Ironically, stowman is a bash script whose only purpose is to wrap git and stow so that you only need a couple of very simple commands in order to manage dotfiles, the automation (i.e. the synchronization task) doesn’t seem to be a part of stowman.