Well my view is since you’re getting small discus you’ll need to shelf the water change system. 2-3” discus will need daily water changes till 4-5” so figure 4+ months. So being you’re going this way a fish in cycle is the way I did it. StRt the tank when you’re ready to order fish. Let it run a week so everything is working correctly and you’ve figured out how to change the needed water. Change 70+ percent water the day before delivery. Add fish and feed about 6x a day. You will notice the mess at the bottom of the tank and realize why you’re changing that much water.
Yes go with a 75 or better as your main tank. But your grow out tank will only need to be a 55. So this gives you time to set up your main tank. Now you’ve got those 2 tanks and a 20-29 will be needed for a qt tank 2 better
. For me I started with media from my community tank. I trust my tanks and it worked out fine.
Ok now since you’re new to discus the much better approach is to buy large fish. 5-6”. Yes more money up front but you get exactly what you want. Not a picture of what they could look like. Plus being full grown you can add them right to your main tank and now you’re off keeping discus
. In a 75 start with 6. Keep them for a year before thinking of getting more. Getting more should also mean more tanks
. Your chances of being able to keep large discus is much easier than small discus. In the end the small discus will cost more than spending up front on the large ones. Much less stress
. If buying discus now all I buy is 5+” fish.