well the first and most obvious thing to do with one of those tanks is to box it up and ship it to me. you definitely dont have time for two big tanks and dont need the hassle of trying to sell it so I'll take it off your hands free of charge lol.
first tank an umbee pair. or a mff red terror group with maybe a lima shovelnose cat or big pleco.
second tank would be a community. severums, acaras, a couple plecos, silver dollars, a shoal of ornate pimelodus and a group of geophagus for sure. if its a tall 500 a school of chalceus or brycon falcatus would be really impressive for the topwater.