Oscars will out grow your 75 gal quickly, you could probably get away with one. Never really liked parrots, they're a genetic hybrid.
I allways kept large groups of smaller/medium sized south central american cichlids in my 75, Bolivian rams, sevrums, sajicas, convicts, fire mouth and some others. There's some disputes but no one ever killed each other, always had many places to hide. The other nice thing is with that group I always had a mix of cat fish and other odd balls in there too and they all got along for the most part