I am going to build a router with OPNSense (in Proxmox, on an HP thin client). I am stuck with setting up the networking (I have the Inel 4-port card). I don't really know how to get started. Right now my device has one LAN cable going into it, and my consumer router is doing everything. I can set up a bridge for the other ports, but what IP address will I use for the LAN? I can't use 192.268.0.1 because that will collide with my consumer router. Do I just take my consumer router offline while I am setting this up?I'd rather not because for sure I will get stuck and will want to look something up online. I guess I could use my phone but not the best when I am trying to see someone setting up something like this.

Silly question, I know, but I just can't think of a clean way to get this going with minimal disruption. In a nutshell, what's a good strategy for setting up and testing the OPNSense while it's not actually doing any routing and then seemlessly drop it in and start working on it?