Had this from a friend :- 
"Hi Gina, came across this just now. Looks like there might be a way to run multiple servers on a Pi using different port numbers. www.youtube.com/watch?v=RwKkLniEIIk "

Wondered if this could be done with Astroberry Server.  Though maybe the reduced software approach would be better.  Seems to me that running 3 instances of Astroberry Server on one RPi 4B could be pushing it.

Just ordered an RPi 4B with 8GB RAM for testing.  I know I can run Raspbian OS Lite and install 3 instances of indiserver and drivers.  That would be a lighter load than trying to install 3 instances of Astroberry Server.  I don't need all the apps included in Astroberry Server.  The big advantage of Astroberry Server is the ease of installation and setup.  I'm happy enough with a piecemeal installation - done it lots of times.