Good for you for doing the research..
There right no ADF's. a 20 gallonis about the biggest tank to keep them in, pus there food (frozen blood worms) are prized by discus and they will never eat.
Discus have come along way and by that i mean they are locally breed in a lot of areas so they are happy in the water of your area and don;t need all the pH monitoring.There happy and ready to go in your existing water. Just call around and see you has them.
For discus to be happy you need about 5 of them.
when there young that tank will be great but as they get older plan for at least a 72 gallon as they grow dinner plate size and may look at little cramped in there.
Hmm...I think you're fine with the fish compatibility except for the ADFs. A 46 gallon is probably too big (yes, a tank can be too big!) for them. They breathe air by swimming to the surface of the water, and if the tank is too tall they can drown. They aren't very good swimmers. As well, the discus will probably bully the frogs...and even eat them. So, I'd just avoid the frogs altogether. (:
Other than that you sound like you've done your research. But, if it were me, I'd get a larger tank if possible...
I am SO happy someone has done research! I could literally hug you right now. I really can't offer help on these fish since it's out of my territory. But If you feel comfortable about your knowledge then I say go for it.