In theory you should be able to use any ports you like, as long as they don’t conflict with other services. Looks like the default port is 3000 according to the docs, so I would set 3000, 3001, 3002 etc myself.
To see which ports are in use by other programs, run sudo lsof -i -P -n
If you cannot get the SL code to work, it may be worth trying to use socat to route usb connections over IP and back to USB