From Rick:
Well the master doesn’t age really it is always in the exact state you left it with the exception of plugins not being updated.
Periodically you may wish to add a new plugin or replace one editing your startup point as you grow.
Spinning up a new dev site if it is hosted on the same cpanel, you would 1st create the domain (sub.domain), then trigger the SSL install to it using SSL/Status, then go to Softaculous and open the list of installs… find your kickstarter and select the CLONE button… which is a new install of that WordPress at the location you choose. So then drop down the URL choice and select your new dev domain to intall to. That’s it!
We are always happy to do it for you as well when you are in a hurry, but I know you like to learn new stuff and stay on top of things.
Rick