2nd Router for iOT and Current Home Network

I want to add a new less expensive router next to my current Nighthawk Model R7960P for 2.4 GHz access points for all my iOTs and possibly additional Ethernet IP connections. The 2.4s work fine with the R7960P but I think I should have a separate access point for them.

All three home Macs are connected with Ethernet although the new Macbook M1 Pro and an older iMac also have WIFI capability.

The computers use manual IP addresses with DCHP but I do carry the MacBook into other rooms / outside patio close enough for the 5 GHz in the Nighthawk.

If I set up 10.0.0.X for the new router, and the Nighthawk using 192.168.1.X doesn’t that mean that my Alexas, bulbs, Rings etc. wirelessly attached to the new one are at arms length and double-protected from the Internet?

Even if I use the same SSID and password for the new router won’t our iPhones need to select that one to check cameras, etc. and then we’d need to change to the original network for the TVs, AV receiver, etc?

And would using 10.0 etc. on the new router mean that any devices hard-wired to it (computers, printers, etc.) would be on a different network and not be seen by my current Nighthawk / network with smart TVs, a soundbar, AV receiver, etc. now connected to the 192.168.X.

Is there a way to connect them for accessibility and still keep the 2.4GHz separate? I’d sincerely appreciate suggestions for the new router, and instructions (including explaining where my logic may be faulty) for what I would like to accomplish. I could be over-, under-, or not-correctly thinking this out.

Thanks in advance.

Rick SEPA