It is incredibly easy to add many wordpress (mini) droplets when creating a configuration. However, how can I add another wordpress install to an existing configuration?
I found complicated apache and wordpress articles. Is there a simpler way?
There's a few options. You can use a control panel to manage your sites, something such as VestaCP (free, open source) or cPanel (commercial), though you'd need to install these on a new Droplet and then migrate the sites over.
There's also scripting, such as using a bash script or you could use any programming language that is capable of running from the CLI. You'd simply create a script that automates creation based on input.
There's multiple ways of doing it, but at the end of the day, control panels and scripts just automate what you'd normally do from the command line, as shown in those guides.