You are meant to find them yourself, what is the point in playing if you just start with everything already?

Where is the sweet spot? For example how does mp10 nightmare cathedral compare to hell mp0 cathedral?

Run the game as admin as it needs special access to write to the program files folder. Modern games avoid that by putting saves in my documents folder but this one doesn't do that :p

If you managed to beat normal mode hell (13-16) then that's the best place to farm, until you are ready for nightmare.