Yes. But be aware that the “versions” are the snapshots not the files.
If you have
--keep-versions=1 and make a backup, you will only have that one snapshot (whichever files were present at the time). If files are missing on the next backup, they will go away from the backup.
I think you can easily set this to something larger, as Duplicati 2 is designed to support exactly this use case: large files that do not change. It does this by applying de-duplication, meaning that replicated data is only stored once. So even if you have 3 backups of the same file, it will only take up the space for storing 1 copy.
Duplicati does not support the sync-like setup that would give you true 1:1 copies.
Yes, that is correct.
Duplicati 1.3.x was based on the same idea as duplicity (hence the similar names) but with 2.0 we changed everything to avoid the long chains and expensive (in terms of storage and bandwidth) multiple copies.