I remember when 120 was HUGE to me, so go you! Welcome to the hobby! You have a great size tank, and totally the right idea for getting started.
So, here is what you have going on: Your Oscar is going to get very big very quickly. They're like big, obnoxious dogs. They crash into everything, break everything, eat everything, and hassle the crap out of everything, as a rule. Of course, there are exceptions, but... And don't get me wrong, I love them, but if I had to desscribe them in a few words, that would be it.
The convicts, if you have a pair, are going to grab an entire side of the 120, or take up a good size space right in the middle. They're going to fight to the death to defend that space so they can breed.
The JD's probably won't act much different, and they aren't going to appreciate being told to bugger off by the convicts.
The silver dollars are fantastic dither fish, which means they will spend their entire lives being beaten up at random by everyone else in there, aside from the pictus, who will probably just hide, not at all impressed with any of it.
If I were you, I would consider a different stock list.