I'm going to make a presumption that you mean a pond and not an aquarium.
How large of a pond are you thinking of? We have several outdoor ponds, ranging in size from 75-6,500g. Only the large pond has power to it, due to a large stream that needs a pump, and a skimmer. Size will be a major determinant as to what type of fish you put in it, as will your growing zone. What part of the country (world) do you live in? Will the pond freeze in winter? If so, what will you do with the fish then?
Koi are warm water hardy, but require large amounts of water. In a 500g pond, you could maybe have 2 koi. In smaller ponds, fancy goldfish do well, and plain comet goldfish are cheap, hardy, and fast growing. Or, you could always try fish native to your area.
As for plants, there are several websites about garden ponds that can answer what type is best for what you plan.
3g betta, 29g molly, 90g Amer cichlid, 90g community, 137g African cichlid, 220g water garden, 6,500g koi pond