Oh boy, you have no idea what some of us are doing. First of all I wouldn’t let those idiots touch my router settings. The misconfigurations I have seen with not just my ISP but with other peoples. Those incompetent fools don’t even change default passwords. Many of the routers from ISP’s are garbage and they want you to pay a monthly fee to rent that garbage.
I once spent an hour on the phone for them to diagnose a problem I already diagnosed. The modem I was paying them a monthly fee for was broken. All I had asked was if I could bring it down to their office and swap it out. Even after I performed every diagnostic they asked for and they couldn’t come up with an alternate diagnosis they still said I was mistaken. A field tech they sent out confirmed my diagnosis after I sat without internet for several days. They actually wanted me to pay for a service call and they didn’t bring a replacement.
On to network complexity. Mind you my network isn’t close to what other people are doing. I’m only going to go over my primary access point which is a residential device. I also have other AP’s, virtual networks, and switches.
I have around 40 devices. Many have static IP addresses set up manually. I have Dynamic DNS to keep a DNS hostname up to date with my public IP address in case it were to change. I have VPN settings so I can dial back in to my home network. My router is connected to my home automation system via telenet so I can monitor devices. I have port forwarding set up to black hole traffic and allow the VPN to work. I have my router set up for internet fail over. A mobile device can plug into a USB port on the router for backup internet. I don’t keep one plugged into the router but it’s set up so when I plug it in everything works. I use keyword and url filtering. I had parental controls set but my daughter grew up and moved out. I disable UPNP because it’s a potential security risk. I have custom DNS servers set in the router to increase speed and reliability. There may be other things too but I think you get the point. It would take a while to get everything back if I had to nuke my router to factory defaults. My router can be restored from a backup but if I got locked out like the OP a restore wouldn’t be an option.
Forgot: Wireless MAC filters