That’s a very subjective question - disabling encrypting and compression will speed up the backup, but will likely use more space on the destination and be less secure. Since it’s your own hardware the security isn’t such a big deal but the space usage might be.
Keep in mind that even with those items Disabled Duplicati will still create a zip file to store the blocks of data your files are chopped up into - you won’t get a direct “browsable” copy of your source files. (I’m not sure that’s what you’re wanting, but some users do so I thought I’d clarify.)
As for snapshots on the NAS, I think it depends on the NAS and drive formats involved. If the drive format is something like ZFS or BTRFS then they should natively support snapshots through CoW (Copy-on-Write).
Older formast such as ext3/4 don’t natively support snapshots but it can be simulated if you’re using an LVM (Logical Volume Manager).
Of course things are already getting a little complicated - are you running Duplicati on the Windows box backup up some local and some NAS files to a destination that is elsewhere on that same NAS?
If so, then you won’t get snapshotting on the mapped drive / UNC paths being backed up through windows. However, if you’re running Duplicati on the NAS to back up files also on the NAS then snapshots should work with the limitations described above.