DIscus Questions - QT Tank/Plants/Substrate

[The_Desacrator]

So when Black Friday rolls around I will be picking up a 56g and I wanna try my hand at discus. Now these guys go for a pretty penny so I wanted to know the minimum size for a QT tank and how long I should QT the new ones.

Any plants that can go with them? I personally really like Amazon Swords and Anubia nana.

Is black gravel an acceptable substrate or should I go with sand?