You don't need to configure the app server for Support Automation unless you plan to have a decent amount of session traffic, and want to balance the load. If you only plan to have a limited amount of concurrent sessions you likely only need the Main server installed on the Background.
If you decide to only use a Main server, the options manager url should point to the main server host. By default the Socket Proxy servers do not serve web traffic, so you want to serve web traffic some manual adjustments to the server.properties is going to be necessary to make it work.