Agree about the drain pipe and having gravel backfill to allow drainage is key as well. We obviously have enough gravel!Make sure to install drain pipe and have outlet for it. Poor drainage is a common cause of retaining wall failure
For the engineers in the house, it gets fun when you start to calculate the requirements from a load perspective. I'm not an engineer and forget whatever math would have helped me calculate it. What's really fun is how different types of soil change the numbers.Pretty exciting project!!! It's flat where I live in Texas, so I find working on hillsides and retaining walls to be very interesting.