Routing/NAT/FW Rules with routing on L3 switch

[tech101us]

Good day to all...
I've recently inherited an environment where I'm asked to deploy a OpnSense Firewall as the primary device connecting a small client to the Internet. The hardware is a small workstation device connected to a Cisco 3560 L3 switch that is handling the routing for several internal VLAN's\Subnets. Not having a lot of firewall experience (although I do understand routing and switching), I've managed to mostly figure things out. The link between the firewall and the switch is a gigabit ethernet inferface configured as a dot1q trunk. Only two vlans are allowed on the trunk...one VLAN for the network between the firewall and the L3 switch and a second VLAN (L2 only) that is handling the connection to the Comcast business cable connection.

I managed to get things mostly figured out...having to define a gateway that represents the next hop IP address for the internal private networks. I could not define the routes from the firewall back to the internal subnets until I configured this additional gateway. The priority on this new gateway I set at the same value as the WAN gateway. Not sure if this is correct or not.

Then I needed to configure a Hybrid NAT entry for each of the internal subnets, and a firewall allow rule on the LAN interface inbound for all the internal networks if I wanted them to have access to the Internet.

i'm running up against some limits in my skill sets, but think I have things worked out. What I'm wondering here is if anyone knows of any resources in terms of documentation, video, etc. that might help me out in this scenario? Or perhaps some best practices documents.

Thanks in advance...