You'll need to create preview apps yourself. Right now with the beta that means making a real app and publishing your content live in the portal. In our next beta update there will be a dedicated preview button in the portal, and a setting in App Builder, that enables you to build a custom app that will show unpublished content in the app.
You only need one Apple Dev account in the workflow you describe. On iOS you do need to get the UUID of all the devices that are involved in testing. You can use a service like Testfairy to streamline the process. They make it easy for testers to register and for the deployment of the test apps themselves.