OMV to Windows backup

Hello, I have omv installed on my wired n100 DIY 4+4bays NAS as our 14hr daytime home server at our living room for nextcloud/pi-hole/jellyfin/tailscale/airsonic.

I have another wireless i7 5775c 6bays NAS that I'm planning to install windows 11 and use it for media and youtube connected to our bedroom TV and powered on only as needed (4hrs/day).

1. What would be the best file system format for the i7 NAS? NTFS/EXFAT/EXT4/etc.?

2. How do I make files in both system synced automatically monthly?

3. Should I install windows 11 or Windows server on my i7?

4. Am I right to not make the i7 as another server (proxmox/omv/Windows server) as I want to use it like a windows desktop machine for media/YouTube? I also have a bunch of mini PC's.