I don't recommend keeping 1 because you don't get to see all of the "personality" of the fish and you would be missing out if you didn't keep them in at least a school of 5-6, which they need to be in to maintain a pecking order to disperse the stress.
The best size to get fish at for anyone that is an amateur would be 3"+ because they are much easier to grow out and are not as needy. Smaller fish will require more time as they will require more frequent feedings and more water changes. For anyone interested in purchasing discus I strongly recommend purchasing 8-10 3" fish and growing them out in a bare bottom 55 gallon tank. When they reach about 5" you can then transfer, say 8 of them in a 75 gallon planted tank. Do not plan on purchasing discus if you don't have at least a 55 gallon tank. Even then, I feel the smallest tank for them would be a 75 and I wouldn't keep more than 7 in there after having experience with them. There just isn't enough space in a 55 for a group of 5 discus IMO but you could make it work. Larger tanks are better!
Pop, none of these comments were directed towards you as I'm sure you know what you are doing when it comes to discus. I just wanted to inform others of what procedures and cautions should be taken.
