The problem with faults is many are related, bad O2 sensor will trigger a default air/fuel mixture to the engine to protect it and that will trigger more codes up the chain, in your case the lean fuel codes etc.

A bad MAF will trigger a lean engine codes and then the O2 sensor will trigger faults because the engine is to lean and it cant correct it due to the MAF giving incorrect signals. That will also make the engine go into default mode... Make sense? It will change the way your engine runs and having poor mileage is common.

The deal is that there is more than one way to interpret the faults and going about it in a systematic and logical way will avoid spending money on parts you don’t need. There are a few other less common things that can cause these faults, but I’d start with O2 voltage, I got a feeling thats the cause of your trouble.

Good Luck