Actually the world of VSTi is completely new to me, so any information like this is useful. In the documentation it says: "SwarPlug is not a multi-timbral plug-in but depending upon your sequencers capability, you can open as many instances of SwarPlug as required".

So, now that I know what multi-timbral means, it is clear that each instrument that I want to use is going to require a different instance and port.