Which is the firmware for this model original or open source like dd-wrt / openwrt?

Model : Hardware Version : Firmware Version : ISP : Hello, From yesterday my router archer C5 begin to reboot suddenly i dont know why. I reset from the button behind and try to connect by default IP...

i would like to get the mximum speed on the net i have several equipments connected to the router by cable and my phone by wifi.

then should be better use wan ?

where there is a manual to configure wan?

which is the better conecction if i receive internet by rj45 cable?