I made progress, but... A couple days ago, I remembered that there is a stream close to my house where I could drive up and park right next to the water. So, I went and checked it out, and sure enough, there was a gravel/sand bar that looked great. The colors and size were perfect. Then, yesterday, I screened, washed and sifted the gravel. Here's a tip though. When you have to carry a 5 gallon bucket worth of wet gravel or rocks to your house from the vehicle, and then downstairs, it's much easier to divide it into two 5 gallon buckets and carry it in balanced. A month ago, when I collected the rocks, I carried the full 5 gallon bucket down and it wasn't fun. Also, washing creek gravel took a lot more time than washing store bought gravel. It seemed like it took forever. I think that I spent a good 3 hours or more washing it. Anyway, here it is divided into the two buckets:

Then, I took the rocks out of the bucket and sorted them out by size and shape, and set aside the ones that I wanted to be seen the most and arranged them on my workbench (which is the stand that I built for my 100g oyster reef tank).

After that, I went ahead and rockscaped the tank, then filled it with water. This was a test run, to see if the wall held up and the roots didn't float. I also set up the powerhead and checked out the current. It ran perfectly. I didn't use this design to achieve unidirectional flow. Rather this current, along with the spray bar, should simulate a stream side eddy and undercut bank. I didn't take a picture because the water was still cloudy, and, I didn't have my canister filter set up. I will have that done tonight.
I also received the light that I ordered, a Fluval Planted 3.0. I'm really happy with it. I plugged it in, downloaded the phone app, and configured and previewed it. It's really cool. And, the best part is that, remember the shiny look of the epoxy after it finished drying, and I was worried about it? Well, what they advertise is true. It really does disappear underwater. Everything should look great when I'm finally done.
However, and now the but... I noticed that the roots stuck out of the water about 1/4", which is no big deal, but, it would have affected my ability to run the spray bar and shoot water over them to simulate the stream. I thought that maybe, when scaping the sand and rocks, that I just needed to adjust it, so, I pulled out the roots, moved the sand and rocks to the right side of the tank, and stuck the roots back in. And...they float. It isn't bad, but, it's enough to mess with my design concept. So, I unplugged everything and will work on fixing that asap. I pulled the roots out and set them in a container to drain them as water does get inside them. I'm not too worried about that because everything is inert that I used, and it enters very slowly. Although, I'm considering another coat of epoxy on areas where water might seep in, just in case.
The roots float at the top of the fixture, moving it away from the wall and up over the water surface. The bottom of the roots seems to stay down, somewhat because of sand and rocks, but, more because there was less foam used there. So, I think that I can leave the bottom alone, and design some sort of hook and latch system at the top, in the back, out of sight, that will hold the roots down.
Next steps include fixing the roots, draining the tank, scooping out the rocks, sand and gravel, add sand and gravel again, rescape the tank, refill it, cycle it, add fish.
The good news is that the back wall held in place, and is firmly attached. I don't think that it's going anywhere. And, the tank doesn't leak. I was worried about spray foam expansion damaging the glass seams, but, they're OK. And, the epoxy shine disappears underwater.
I'm almost there folks. There will be fish in it soon!