Through my research, I found that most recommend a 220 as a minimum for a fire eel. Of course, bigger is better but this is what I have to work with right now. If they end up getting too big and need a bigger tank than I can provide then I will look for a new home for them.
As far as keeping a ray, that is a big part of why I posted this thread. As I mentioned, some people say a "teacup" ray can be kept in a 125 while others say that even the smallest ray needs 300-400 gallons, some people even say larger.
As far as the discus go, I plan on growing them out from two at a time in a 29 gallon bare bottom grow out tank and then adding them over a few years time until I have a group of 8-12 of them.