There are different ways how you can connect the router to the network.
You could either connect the WANs directly into two ports of the firewall and then connect the firewall to the switch with two ports (setup in a link aggregation). However I like feeding my WAN into the switch instead on its own VLAN (two different VLANs in your case). That way you would only need two 1 Gbit/s interfaces on the router instead of four.
Traffic from the internet would come through one of the WAN links into an untagged switch port, get tagged in the switch, sent through the 2 Gbit/s link to the router, run through the network stack there, back through the same physical links into the switch and from there to the client. This works because 1000Base-T is full-duplex and can send 1Gbit/s in each direction simultaneously.
If you’re looking for HA, this might not be the best setup.