Don't know about the plug but, yes it's best to use the lambda sensors as they monitor the amount of oxygen left in the exhaust.
The hotwire air mass sensor measures the amount of air coming into the engine, the ECU then calculates the appropriate amount of fuel to be injected, the lambda sensor then checks the exhaust gas to ensure that this is correct and feeds this information back to the ECU so that small adjustments are made.
If the Lambda sensors are not fitted then the circuit is an open-loop system (no feed back) with lambda sensors it is a closed-loop system (feedback).