What I feel, there is no need to recreate multiple WAS instances, also there is no need to install Network Deployment Manager. Your objective can be achieved by installing base application server. In case, you want clusters of application servers to support different environments, then you certainly need to install Network Deployment, as base version does not support clustering.
Create separate application servers, or clusters for separate environements (say, dev_server, test_server etc.), create separate virtual hosts to for your environments (say, dev_vhost, test_vhost etc.). This way you can have different URLs for different environments. In case, you have to deploy same application to diffrent app servers/clusters, all you need to do is to change the context root inside ear file.
