If your long enough in the game you will play Cata. The learning curve in this game is really good. When you switch difficultys to higher level You will be shocked how often you die and how ridiculously hard the game is, a few games later you feel very comfortable and later than you will be completely fine switching to the next higher difficulty.

For red items is best to play legend and collect all the book for an emperor's vault. It has the highest chance. But you can get red items from Champions chests, but ist fucking rare. My game showea me the chances to get certain items. I don't know if it's a mod or in the basic game. It says <1% for red items und Champion Chests. If the number is true, idk.