What makes discus hard to keep are how people take care of them. Many folks like to power feed thinking they'll get some crazy 12" growth on them. This is not the case. Genetics are genetics. Unless the discus came from 12" parents, it's not likely that they will excedd the adult size of the parents. Three to four feedings of high quality foods a day are more than sufficient and will allow your water to mainatin it's quality.
Young discus of 1 to 3" do very well on this feeding schedule. Try to space the feedings out equally and stay consistent with the schedule. Your water cahnge routine that you have described should work out quite well. On top of what you are already doing, I would do a large water change once a week. I perform exactly this on a 2000 gallon hatchery.
Discus are more durable than most think. They WILL let you know when their living conditions are not suitable and you typically have time to correct any issues without any serious issues. I am like you as I do not test my water constantly. Once a tank is cycled, it's cycled. That being said, if at any point you disturb the biological media or significantly increase your biological load, then testing your water is smart. You want to make sure that changes that you have made to the tank have not negatively impacted the filters ability to maintain high quality water.
Another item of consideration with discus is to make sure that the tank is overfiltered and that there is plenty of oxygen available to the discus. Some use air pump with air stones, air operated sponge filters, trickle filters, etc. Gas exchange is critical.
P.S. I would get away from using gravel. If you want a substrate, use sand. It's much better for discus. These fish like to forage and gravel makes that very difficult and it's hard to keep clean. Some play sand from home depot looks fantastic!
Hope that helps!
