if it's off when you start up the car again, you don't need to reset it. it will just stay stored for the next time.
The oil is definitely the cause of the code. The first thing I'd do are compression and leak down tests. No visible leaks? Oil pan plug? could be coming from lots of places...

One thing that will cause the rings and bearings to wear out is rev it when it's cold. Before the engine gets to operating temp, it's basically a disaster waiting to happen. Make sure you let it warm up and get some oil in there before you rag on it. Also, driving it as long as you did with that little oil could have caused a lot of damage to the valve train, bearings, rings, etc.