Private or public cloud both works, the prerequisite is docker. There may be technical details to be considered depending on your individual setup (like with every other deployment methodology), but this can not to be ensued remotely.
You should investigate the webMethods Microservicecontainer which is basically the method to support docker but is more lightweighted than a full IS (Development will still be on an IS, so you are reusing your existing code). You should also go for the latest full release, as this technology is rapidly evolving.
About licensing you need to contact your account manager.
One alternative, which I tried myself, is to install the full/required webMethods stack on base Docker image (RHEL/CentOS) and create a base webMethods image out of it.
Use that image to deploy as many instances as required.
It also supports multiple deployment scenarios using Docker Swarm or Kubernetes.