well, I wouldnt reccommend having less than 5 discus, and you should have at least a 90 Gal tank for them..
Any less than 5, and they seem to have agression issues...
Even if you had a 40g breeder to optimize swimming space, the tank would be too short, in my opinion. The only discus I've seen HEALTHY were in 90+ gallon, well-maintained tanks with 4+ discus.