When I set the extruder cooling fan pin, in rambo fan0 is 8, #define E0_AUTO_FAN_PIN 8, I get this #error "You cannot set E0_AUTO_FAN_PIN equal to FAN_PIN."
You cant set the same pin for this. It needs to be two different fans.
one fan is for cooling the fins on the hotend (on most machines this is always on. but can software controled with E0_AUTO_FAN_PIN to turn it on/off with temperature)
The second fan is software controlled and is turned on and off as needed, eg for bridging, or for pla
D8 is normally the software controlled fan for part cooling.
D2 would be your E0_AUTO_FAN_PIN
re FANMUX0... you dont have multiple extruders, (at least your config says this) you don't set this, leave as -1