Depends what you want where.
The media plate is just Ethernet extension leads to the various different rooms.
When you say modem in the garage do you mean modem (ONT) or router (hub)?
If the former, where do you want to site the hub, do you want it in the garage with the ONT or somewhere else?
If you want it somewhere else, you will need to connect the ONT to the appropriate socket on the media plate for the room where you want the hub. This will mean that the other sockets on the media plate are redundant. Then connect the outlet in the chosen room to the WAN socket on your hub.
If you want the hub in the garage, just connect the ONT to the WAN port on the hub directly and then connect the remaining 3 LAN ports to 3 of the ports on the media plate. You can then connect an Ethernet cable to your devices at the outlets in the appropriate rooms.
The first Whole home disc connects via Ethernet to the hub, either directly or via the media plate. Subsequent discs connect via wifi to the first.