Congratz on starting on your road to discus! I love them. Personally, I recommend a minimum of 55g and even better is 75g. I had a 55g for my group, but when I upgraded to 75g I could tell they were ALOT happier. Also I have juveniles and do a 90% water change 6 days a week. Discus are cichlids. It's usually recommended to start with at least 5 and preferably 7+ to spread the aggression around. There are many different opinions and experiences out there. I would research as much as you can.