Possible, yes.
Advisable, not that much (my view).
Is there really no option to have a wire ?
Even (… shivers… ) powerline can be an option ?
If you still want to go wireless, keep in mind you may have to sacrifice one of the bands for backhaul connection.
2.4GHz or 5Ghz (I would choose 2.4Ghz, longer range and better stability when passing walls etc).
So that requirement on merging 2.4 and 5Ghz in the same SSID may not fly then.
Theoretically it can be done, practically it would hamper too much with performance.
WHen keeping AX2 as main router, it doesn’t really matter if you use cap AX or Audience.
However … if you would have TWO Audiences, then it’s another story since that one as multiple 5GHz radios where you can keep one completely separate for the backhaul connection without impacting the other one.
But again, wired connections are BY FAR preferred. Think out of the box. Maybe a wire placed on the outside of the building only passing the walls to get back in ?
Especially when you plan to extend that network, I strongly advise to use wires.
If you keep it wireless, each added AP will drag your performance further down.
G.hn standardizes different physical media, coax is one of them.
When I was looking for a solution for my parents’ house, I settled for MoCA (the 2.5 Gbps variety) simply because of better availability - ethernet over coax is not really popular around here because cable TV wasn’t a huge thing (before it could spread, it went the IP way), so I had to get something from overseas (they did provide power adapters fit for European power sockets). But G.hn for coax were available as well, perhaps even slightly better from technical point of view.
Oh yes, it works great, much better than powerline (also used in the same house).