I am curious about the coco mat. Is it synthetic or real natural fiber? If it is natural fiber I would wonder about what happens when it eventually decomposes. Are you using it to avoid scratching the tank bottom?
The background looks great. Very artistic.
Natural fibre. It's a product intended for potted plants. I am also curious about what happens when it decomposes! Perhaps I'll rebuild the tank before that happens. I like using natural products but I do have some plastic supports in the substrate. Because I'm using rocks I definitely wanted to have support underneath to spread the weight. It's exactly what I wanted for that purpose. It's also got filtration properties and I've used it in my other two tanks. For example, I used it in my Whisker Shrimp tank on one wall to give that guy a way to climb up and hang on. In my Snails and Shrimp tank, I created a deep substrate and I used the fibre mat to create barriers to separate an aquarium soil zone from a filtration zone. Furthermore, it's a bacteria substrate. I really enjoy working with it and it's part of my tank recipe now. I would definitely use it again in a future build and would look for interesting ways to use it.
EDIT: just remembered also, it's a good base for your hardscape, as it holds in place and doesn't shift. You'll need to secure it with aquarium-safe silicone glue first though. This is an advantage compared with using sand since sand shifts around and has a habit of not being where you want it to be. Personal preference plays a part too, I'd never want to use plastic egg crate for example.