Deleting old lrcat and lrdata files

Most likely these are older versions of your catalog, as Lightroom Classic upgrades a copy of your catalog each time there is a new full version. The names of those catalog files often give you a good indication. If you have a 'lightroom catalog.lrcat' file and a 'lightroom catalog-2.lrcat' file and a 'lightroom catalog-2-v10.lrdata' file and a 'lightroom catalog-2-v10-v11.lrcat' file, then it's almost certain that the last one is your current catalog and the other ones are old catalogs you can trash. You could try to open these old catalogs to double check that, but that won't be possible without Lightroom Classic upgrading a copy again. That means it's up to you to decide whether you trash them without verification, or keep them as a kind of backup. Catalog files are not that big, and you could move them to an external drive to save space. Old lrdata files can be trashed safely because they can be rebuilt if and when needed.

Am I right in saying I can safely delete anything other than my current catalog and previews?  

You can certainly delete old previews. As far as catalogs go: You might be right. You might not be right. This is something you have to figure out, as we don't have access to these files and we don't know what is in them and we can't give you a blanket statement that you should or should not delete them. You should determine whether or not any of these .LRCAT files are still needed by opening them and seeing what is in them and confirming that you have these photos in later catalogs.