HOWTO: Test/Setup Protectli/Opnsense on existing 192.168.1.1 router

[rl]

I have an existing router that is at 192.168.1.1. I wanted to set up the Protectli/Opnsense box on my existing network just to set most everything up before yanking out my existing router and then struggling to configure the new one in a panic.  I couldn't find this documented anywhere, so consider this my personal experience.  Being done on a Debian box with Spectrum Cable as the ISP.

1: Forget the serial connection.  Connect the Protectli/Opnsense box to a monitor/keyboard/mouse.  Also connect a patch cord from a laptop eth port into the LAN port of the Protectli/Opnsense box. Turn on the Protectli.
2: Log into the console as root/opnsense.
3: select (1) Assign interfaces if your LAN is not already set to igc1 and WAN as igc0.
4: select (2) Set interface IP address, and establish igc1 LAN as static 192.168.168.1 with /24.  Continue to use https as web gateway, create new certs, don't use dhcp, don't reset webgui. 
5: On laptop.  Confirm that wifi is off.  Eth cable is connected to Protectli box.
6: Enter these commands:
    `sudo su`
    `ip a`     # to determine your eth device name mine is enp7s0f1
    `ip addr flush dev enp7s0f1`   # use your own ethernet device name instead of mine
    `ip addr add 192.168.168.10/24 dev enp7s0f1`   # this sets laptop IP to 192.168.168.10 temporarily
     ip route add default via 192.168.168.1`
    `ping 192.168.168.1`     # you should be getting response from Protectli now.  Ctrl C to kill the ping.

Now, you can open a browser and point it at https://192.168.168.1.  You may need to override browser security attempts.
If no access, go over to the Opnsense console and select ( Shell.
Enter this comand to temporarily turn off firewall:
    `pfctl -d`

Try web gui again.
You should now have access to the web gui.  Go break something now....