In a L2 Speedfusion setup, Peplink devices only act as the bridge between your offices. The one handling L3 routings are usually the core switch sitting behind your Peplink devices.
An additional Peplink in HQ in a HA setup will be nice, considering your traffic are all routing via HQ.
This should be in a star-topology.
Balance 710 will be connected to the Balance 380s.
Balance 380s will be connected to their respective BR1s.