Whew! Thanks for bailing me out, glens!! I've made some progress (in a fumbly way). I unplugged and re-plugged the main router, and tried to do a WPS reset on it. (I was relieved to see the LED light.) Then, I tried to proceed as though it had been successfully flashed. I rebooted the modem and connected it to the main router's WAN port, shut my computer down and turned it back on, connected the main router to computer with ethernet cable. The ASUS Welcome page came up, and I chose "set up new network". I tried to get it to detect the node, but is said it couldn't find it. But then when I went forward, and set up the SSID and the router login info, and it showed me the network, and it seemed to have the node attached by AiMesh. On the Admin>Firmware upgrade page, I could see that the node was on GNUton, but the main was still on Asus. So I flashed the FW, and this time it worked!
I am thrilled to have internet again, but was too nervous to continue with any more steps tonight - don't want to lose internet again! (Thank goodness, my cell signal - very weak at my house - was strong enough for me use to hotspot my ipad and computer. There have been times when I've been without any connectivity.)
I need to remove the ethernet cable that is still connecting my computer to the router -- I can just remove it, right? The computer shows it is on the wifi network (as well as ethernet). And then I need to move the node to where it actually is supposed to be.
And I need to do the final WPS reset on the main router - I really hope that won't screw anything up. Will I have to go thru the whole Welcome/QIS setup again?
Given that I am on GNUton-Merlin software, should I check yes or no for Administration>Firmware version>Scheduled check for new FW?
Then, I have some more questions, if anyone has the patience for them. If I set up a Guest Network - should it be 2.4 or 5 gHz? Do I need a separate Guest Network for each device (eg, smart TV, internet radios)??
If I don't enable AiProtection and Network Protection (because I am not comfortable with Trend Micro's privacy policy), are there other security settings I should set? (I plan to sign up for a paid VPN, and add that.)
Thanks again SO much!