This is an easy one. I have configured my OpenWrt successfully as an access point only. Everything is working like a charm. I want to explore what else can be accomplished under this configuration. Could you please send me some links to read about possibilities? Or at least mention them so I can google over them?
is not supported by OpenWRT, it receives optic fiber and the TV decoder are connected to it. So I cannot get rid of it. The WiFi provided by this modem it's really awful, that's the reason I bought this router and configured it with OpenWrt, obviously the WiFi is turned off on this modem.
The Archer C7 isn't really ready for gigabit service, the CPU is not very powerful.
In general when you go to a two box system you want to dumb down the ISP modem / router as much as possible so it becomes a dumb media converter from Ethernet to fiber or DSL or cable or whatever you have. Your OpenWrt box will do your own routing. Then you can set up things like a guest network or VPN server (though VPN server won't work at real high speed due to the CPU).