How to best setup my system

I just had Fiber installed with BGW320-500 which connects to 32 port network switch that feeds all wired connections for the basement and main floor. On the main floor, I have Asus RT-AC3100 router that I utilize for wifi.  So do I need to put the ATT gty in IP passthrough b/c right now I'm not getting eveabout 200 Mbps on my Apple computer when I run speed test even though it is connected by ethernet & my wifi speeds I say are about same?    I am connected with the ASUS wifi that I did factory reset on to finally get it to show an internet connection after original install.  Is this router good enough for the fiber connection or should I look elsewhere and maybe to mesh to even get better reception upstairs. 

i forgot gtwy does not connect directly with switch, I have ethernet that I connects to it and that goes to the router upstairs then cable that comes back to from the asus to switch which is weird not sure why that is and was same way with old spectrum setup.  So should i connect directly from ATT gtwy to switch instead?

thanks

chris