Hey!! Welcome to MFK!! Tis great gettin new members!! Glad you decided to take the plunge!!
About your tank....it could work, but given those dimensions, its gonna look pretty crowded in there. Oscars and Tex. both push the 12" range easily...and having several of each species, can really make it cramped. Plus your bioload is gonna be off the hook...lol. In reality, I would advise against it, but in the end its your call!
There are a 'few' other options for you though!! It all really depends on the type of tank you want. From the ones you listed, sounds like you want a 'predatory' tank. The poly's are a must, so they are always gonna be in the equation. Overly aggressive fish are out, so Parachromis are gone.... Gave you ever considered a Satanoperca or Geophagus tank? Or possibly a Thorichthys tank? They are great fish, full of color, get relatively large, aren't that aggressive, and would work perfectly in that size of a tank! Just a thought....if you like it..we can go from there!
I havn't thought about a geophagus tank, I had firemouths a few years, and am looking for something different. The geophagus tank sounds interesting, they might make a good display tank aswell.
why not go for some thorichthys mixteco blue or ellioti's they grow to be real nice and you could have sajicas too or blue acara if none of the above suit you could go for a gt or (maybe and) jd. a jack dempsey would be my first opion and you could keep them with other simular sized cichlids. gl in what you pick