Configuring Remote Home Assistant - Making remote items show up

I’ve just managed to get Remote Home Assistant (RHA for short) working on my LAN. I have two RPi4s. Pi-B, the remote one (B because it’s in the barn) and Pi-H (in the house), that’s the main one. (They’re on the same LAN, connected through underground fiber optic cables, but too far apart for wifi to work through our dense forest. Not using ZWaveJS2MQTT because I’ll be using other control systems in the barn and house.)

The problem I’m finding now is the configuration of the remote system. There is a 4 step configuration dialog that involves settings for filters - both to include and to exclude. I’m not clear whether a device from Pi-B (the remote system) would be included automatically (doesn’t seem to be the case) or excluded automatically. I’m also not clear what I’d need to include to make a dimmer, for example, on the remote system to show up as a device on the main system and for its current state to show up there, as well as for it to be able to be controlled from the main system. The documentation for this part of the configuration is sparse. There are examples for configuration.yaml, but I’m still not clear on just what I need to do to include a device and all that’s associated with it so I can read the state and control it from the main HA instance on Pi-H.