Best file system for a storage server

Hello everyone, I am fairly new to ubuntu and I am bit at lost with the different filesystems and I was wondering if someone can help me
I built a 32GB ubuntu 18.04 server with 3 Disk 1 of 500 GB and 2 4TB disk. Ubuntu has been installed in the 500GB drive and it is format with ext4
This server will be use 90% of the time as a backup server.
Backup for an Exchange Server
Backup for pictures/images/drawins
Backup for user home directories.

Everyone of the systems above are windows system.
I will need to mount the linux filesystems (located on the 2 GB disk) in the windows systems in order to copy the data from Windows to Linux, hence using samba in the ubuntu server.

Of course if any of the windows servers fails, I need to be able to copy the data back from Ubuntu into the given server.

Question here is, should I need to partition the 2 4GB disk to NTFS or Ext32 or ext4 is just fine (or any other fisystem for that matter?)

thank you very much for the help.

I’ve moved this to the category because this site isn’t designed to take tech support questions. Sorry. I’d recommend using one of the official support channels listed on the page