1. Discus will breed in a large tank, but they usually will breed more readily in a small tank. I prefer 37 gal cubes or 40 gal breeders.
2. I tend to reduce the water changes if they start to clean a surface - typically 10% just to clean the gunk off the bottom. I will increase water changes after spawning.
3. Very little chance that any free swimming fry would survive if you have tetras swimming around.
4. No need for special lighting or any coverage until they spawn.
Good luck, Willie