What we really need to know then is, is this going to be a feature in your house? Is it your only tank? You say you are not new to fish keeping then perhaps the Discus idea isnt so stupid move on to some thing new and a little different there is some superb info on them on here. Or did you really want that one odd ball tank? If so I love Oscars but they are bread and butter common as muck I love them in a big tank with other fish but always feels sorry for one or 2 on there own. As I said a 125 is a nice size planted community tank but sort of limits you to I large nasty fish. If youre going to do that I would go really odd something like Frontosas like a breeding colony lots of colour again would look cool with plenty of rocks in it. At the end of the day what are you looking for out of this tank?