Completely your call, the link/guide that you shared in your original post looks like it has almost everything you need, other than you will require a key generated from Vera, rather than as the example does get it from a HomeAssistant (Docker) container.
The link I shared had a post on how to generate the key and send it to a raspberry pi, so in your case you could just send it to your ReadyNAS (or into a share) instead to them find and import.
If you are concerned about the ‘dropbearkey’ command then just look here - dropbearkey: create private keys for the use with dropbear(8) or dbclient(1) - Linux Manuals (1) where you can see the -y and -f options are just coping the key to a file, grep is then getting that information from the file and then - it goes on to ssh onto the pi, create a .ssh directory (if one does not exist) and then it write the information into ‘ .ssh/authorized_keys’