Patio pond

paradise fish would do well, reproduce MUCH more slowly than guppies, and come in all kinds of colors these days

watch out for raccoons, they like a good sushi bar

i agree with the loach -- goldfish are Very messy, will eat your plants, and will quickly outgrow your bowl

isn't that a little small to try to fit a liner into? you might consider waterproofing the inside instead
 
An air pump or a heater aren't required. Keep in mind, however, that the guppies will overpopulate the pond; alternatively, you may try a larger pond, such as the one I have, where you can keep whatever fish you like. It was a very good buy bought it last year only.
 
AquariaCentral.com