Now that we have the initial question(s) answered and settled, and sorted out that the tank is suitable for the fish, I'd like to comment on a couple of very valid points made in this quoted post. They are things all of us must continually keep in mind.
Fish cannot tell us they are happy, and there is absolutely no way we can ever know they are "happy." All we can do is research what the species requires in terms of its environment (environment meaning every facet of its life), and do our best to provide it or a reasonable facsimile. "Requires" equates to "expect;" each species expects certain things in their environment, and these expectations are programmed into the fish's DNA. None of us can change this, we can only learn the expectations and provide them. When we do, we may assume the fish will be "happy."
Like most living creatures, fish will try to make the best of what they are forced to endure. The will to live in animals is indeed strong; just look at how dogs, farm animals, captive animals that are horribly mistreated will live on. Anyone who thinks the animal is "happy" does not know much about animals. Eating, swimming and even spawning is no guarantee that the fish is even healthy, let alone happy. Eventually such conditions will kill the fish, either through a shorter lifespan to by succumbing to disease it would normally be able to handle.
Turning to the substrate, there is more to this than just the roughness though that is crucial. Bacteria lives in the substrate, and a fine substrate like sand provides the best bed for bacteria and fish will have fewer problems related to bacteria. Corydoradinae species are filter feeders, something else that is programmed into their DNA. They take in a mouthful of the substrate, filter out food, and expel the substrate material out via the gills. Some of it gets swallowed with the food, and passes through the fish. None of this can occur with anything larger than sand. And nothing but non-angular smooth sand can assure the fish will not have internal problems in the gill filaments of through its digestive tract. Add to all this, every species of Corydoradinae in nature lives on a sand substrate. There may be rocks and boulders but there is sand in between, or mud. All of this is fact.