Fiasco or World Wonder?

I'm still working on a project I conceived more than a year ago. A drain hole exists in my backyard that lets water from the neighborhood pour down a long subterranean tunnel into a retention pond at the far end of my 'hood. When I had no kids this was no problem, but after my first was born I got to thinking that if a kid got in the hole it would be bad... so I covered it with a steel grid to keep people out, but let water in.

The hole itself was surrounded by an impenetrable wall of blackberry bushes - which made it less subject to kids, but more dangerous if a ball went over this hedge and needed to be retrieved. To shorten this tale, I conceived of a way to convert the weed and thorn filled hole into a tiered vegetable garden.

At long last I'm making progress. Here are some shots of "before" and current work on the project.

I intend to re-do this in stone at some point, but doing it with lumber is about $300 cheaper than the dry-stack masonry I prefer.

This is a BEFORE view of the project after a neighbor kindly used a bobcat and took down the blackberry bushes for me. I installed the silt fence and began to contemplate what I could do with this. You can get a more detailed picture by clicking on these. My plan was to setup two tiers of garden rows, and then setup some stairs opposite the drain hole. This crude drawing is what I've been working from.
Here you can see the wooden structure. Those walls are 8 foot long 2x4's which gives you some idea of the scale of this earthwork project.
Here's a view of the before state, facing the drain hole. When I'm done, this photo would be taken from the top of the stairs.

Here's the "current" view of progress. I should be able to get plants in within a week barring unforeseen circumstances.
The steps themselves may be the hardest part - but if the Egyptians could do it so can I. Because I've seen dozens of documentaries and I know that when I'm ready, UFOs will appear and beam the steps into place - then give me secret knowledge. And tomatoes. Just in case they don't show up, I'll keep working using shovels, picks, and gloves. (But I just know they will. Aliens love tomatoes.)