From my dealing with these cars for over 10 years , the upstream 02 sensor heater is pwm if you look on a scope and it measures the current , at idle the exhaust is not hot enough to keep the 02 sensor hot enough , i have never measured it under hard driving , but WOT it will be ignored by the ECU , it uses a PTC so as it gets really hot the resistance goes up and the current goes down so the heater doesn't melt, down stream 02 sensor normally has nothing to do with fuel trims just cat converter efficiency , yes you need a knock sensor other wise the ECU will pull the timming , it has a bias voltage which the knock sensor modifies it and with out it you will have a high voltage code , always go bosh OEM for subaru sensors otherwise it will act weird and you will end up chasing something else , i am just guessing but maybe 1 to 4 amps for the ECU power consumption , the data line is around 5 volts if i remember right , the speed sensor is a 3 wire hall effect sensor and is located on the side of the gearbox