So an update.
New router is working fine.
And to make installation painless, did the following.
Shut down Cable modem.
Disconnect cable modem from out router, and connect to new Asus router.
Turn on modem, wait a bit, turn on router. Connect PC hardwire to router, and set up router, and get the new router working for wifi.
Now the trick.
I connected my old router WAN port to an ethernet port on my new router.
Power up old router, and now I have both new and old routers working.
I gave the new router wifi different names from the old router wifi. So I can see both old and new router wifi channels.
So all of the devices that were connected to the old router are still connected to it, and work fine.
I asked my daughter, and she said she didn't notice any change in speed after I did this. And she listens to spotify and watches a lot of video, so speed is unchanged with this setup.
And my old setup includes two routers setup was a wireless bridge. My audio PC is connected to the 2nd router, so it can connect ethernet without running an ethernet cable from my main router (which is not really possible) The 2nd router still works fine too.
I may migrate some devices over to the new wifi, but I can do it was I see fit. But changing like this made it really easy, took about 10-15 minutes at most.