@jaleman.ht,

If I am reading this correctly, either way will work and will simply change how your network traffic is "funneled" up the chain to the main node.

If you add the powerline adapters to a switch, you will be sharing the same ethernet cable on the way back to the router. 

Something to keep in mind, is that you probably do not want your entire network dependent on the Powerline connection as it is subject to more interference than traditional cabling. If something were to happen to the powerline network you want to ensure that your network is still connected to the internet and that the main node has an active connection, this way only the powerline connections will fail, and the network can easily recover and reestablish the powerline backhaul.