DHCP/Overlay Network issues

Have some questions answered when it comes to setting Firewalla Blue to be the DHCP Server for the homes network and how to configure the overlay?

Current Networking gear in the house

1. NBN Modem/Router - Internet Source

2. Ethernet Switch

3. Wireless Access Point for Rear of house

4. Firewalla Blue box version 1.956 - in the beta program and I am also using the beta App release on iOS

Firewalla is plugged directly into the NBN Modem Router in LAN Plug 1 the cable going to the switch is plugged into LAN 2, the back AP is run through the ethernet switch.

currently, our overlay network and primary network are set to the same range. Is this wrong? I also cannot seem to get any port forwarding to work in this configuration.

Earlier this week we got the NBN put in so I was going to switch the primary network setting of firewalla to match the new modems and then leave everything the same but when I did this both the NBN Modem Router and the Back ap were giving out IP Addresses in the Primary network range rather than the Overlay?

So I have reverted it to having the primary and overlay being the same and from what I have been reading this shouldn't be done like this.

so basically I need peoples help. Where am I going wrong?

should the firewalla be plugged into the NBN Modem Router or should I plug it into the ethernet switch?