Oscars grow quickly and with a 75 gallon tank you can possibly expect your 'runts' to start putting on size at a rate of 1" per month. You really can have tankmates for a short period of time since you will have a big fish on your hands in a year. I recommend just the one Oscar and a single featherfin cat for clean up.
I have a single bumblebee oscar going on 10" and a 4.5" L114 pleco in a 72g bow with an AC110 and Eheim 2217. Its tough to keep up with the constant mess this fish can make so I have an idea of what you would be realistically facing....
I have a single bumblebee oscar going on 10" and a 4.5" L114 pleco in a 72g bow with an AC110 and Eheim 2217. Its tough to keep up with the constant mess this fish can make so I have an idea of what you would be realistically facing....