well two should be good, what i would do is buy six,sourced from different locations and grow them up together until they pair off, then rehome the others,,,as for dithers,,, tinfoils/dollars/birchirs/etc etc the skys the limit to a degree,,,,,
i have 3tinfoils/1spotted dollar/3tiger oscars/1 golden saum/1 gibbcep<sailfin plec>/1senegal birchir/1 chinese algae eater/1 hoplo catfish/2clown loaches
this is in my 60inch/24/24inch....filteration has to be very good, and keeping up with the waterchanges
three oscars is not a good number so dont do this, iam ready for anything happening,,,