One thing you should definitely do is move the Backups folder to another drive. Backups MUST be on a different drive than the originals. You really should set the option in backups to store future backups on a different drive than the originals.
As far as reducing the number of other catalogs, you need to LOOK AT them with your own eyes to determine if you need to keep them, or not. No one here across the internet knows what is the difference between catalog fluviatilis-v12.lrcat and catalog fluviatilis-v12-2.lrcat. So you look at these catalogs and see what is in them and decide if you need to keep both. similarly, your -V11 catalog may be redundant and not needed, but I don't know that ... you have to look at it and decide.
A good idea is to MOVE, not DELETE, some of these catalogs to another drive just in case you might need them in the future.