I'm going to be keeping discus again soon, but for my experience make sure to keep your discus hot! Not extremely hot but 82-86 with 84 being the sweet spot. Unfortunately, hillstream loach and discus will not work as the water needed for each is different, however a good replacement would be sterbai corydoras, or a bn pleco. Remember to keep the water very oxygenated with aeration! Tetras can be a bit challenging with discus, I kept rummy nose and cardinal tetras with my discus at one point, but do know that you will have to grow them up and replace them often as high heat tends to reduce their life span. Also with discus, if you are getting them young less then 4 inches, it's highly recommended to have a separate grow-out tank and grow them at least 4 inches or bigger and then introduce them into main tank as small discus tend to grow the fastest so wc and good food is highly recommended! Good luck!