ML-Always happy to try to help.
The rule of thumb in the aquarium biz is 1 inch of fish per gallon max. Most of the exotics you plan on using probably average around 10-12" full size right? (texas Rios, Tilapia, GG, Golden BG) the exception is the pacu. (3ft+) I myself would not recomend pacu in a micro pond because eventually just a few of these behemoths will exhaust your little ponds carrying capacity. Unless you have a plan for them once they reach a large size. (donate to city aquarium or eat them) Keep us posted!
P.S. Will your winter temperatures support the pacu? I guess not if the Tilapia die each winter. If the pacu don't survive winter temps, you might be fine with just a year of growth.
P.S.S. Another possibility might be to heat such a micro pond in the winter to keep the fish through the year. I am sure there are pond heaters for ornamental ponds. These might be able to keep your pond at acceptable temps for your exotics year round.
So many possibilities! Bring on any other questions and keep us posted with the progress.
