yeah, go with some real colorful killis. just make sure you cover the pond with bird netting, and research as much as you can as far as what species you want, their conditions needed, and talk to lfs about what killis they might like
well no lfs that i know of would want to buy eggs. however, even if you grow them out an inch or 2, i'm sure you could sell them to some stores. i think this comes down to which species you choose as far as leaving them in there 4 seasons. if you add a heater, i don't see why you couldnt
these are some very nice non-annual killis. remember, non annuals live longer than one breeding season, which could also help your numbers theoretically. this site has a lot of info on killi species. you can at least figure out what you like and google them further