Using a trough is pretty straight forward and can be easily setup. Just make sure its somewhere that's not in the sun all day (shade will keep the temps more consistent) and that you have plans for predator protection and possible freezing temps.
Filtration can be something simple such as a floating pond filter (@$100 at Home Depot, etc). These filters typically have UV feature and a small waterfall option to keep the surface agitated for oxygen. Or, you can consider something a bit more complex such as a bog filter that utilizes plants as the filtration system (check out this thread:
http://www.aquariumadvice.com/forums/f135/ryukins-in-the-backyard-pond-257101.html). Middle range would purchasing a pond pump and making a filtration system or purchasing a pond filter that sits independent of the pond.
Pond plants, especially floating types such as water lettuce or semi-floating plants such as parrots feather, are easy to add and require little maintenance.
For the winter, a stock heater is not necessary as these are intended to heat the entire tank to keep it from freezing. A simple de-icer would be more than sufficient to keep a section open and unfrozen.
Predators can be avoided with a simple net over the top. Pond nets can be purchased for under $20 on ebay or amazon and for something this size, they would likely cost under $10.
Please ask any questions!!
