I have a slope about 11ft deep by 5ft high. I'm planning on terracing the area into 2 levels. 5.5ft wide and 2 ft high. So 3 walls 2 levels. My plan is to use pressure treated wood. 4x4 as posts every 4ft and 2x8 boards behind them. I live in Southern california so don't get a ton of rain. The ground is full of large rocks.

My quesion is do I need deadmans or other extra enforcement? Or should I be OK with the cemented posts every 4 ft? Also any advice on stairs would be appreciated. Thanks in advance