OH fo sho. They are very rugged and can handle anything that comes their way...inlcuding a puddle in Japan (which is where they originated...look it up).
Most likely.
Pleco's are tropical fish, so if your pond has a sub-tropical temperature, the pleco will not survive in the pond for very long.
yes
If you are asking if they can live in a cold outdoor pond than the answer is no. They come from a tropical climate in South America and are not meant for water below about 72' Fahrenheit (22.22' Celsius).
Better than what? I don't know exactly what you mean or why you ask, but bettas (assuming that's what you mean by fighting fish) need clean, chlorine-free water that is above 76° and filtered and at least 5 gallons to swim around in. You can't keep them in an outdoor pond and water taken from a pond is likely to have diseases that will kill them.
Pictus catfish are a tropical species and will not survive in an outdoor pond unless you live closer to the equator. If you live in the continental U.S., the only place it may be able to survive would be in southern Florida.
Three types of forest populations that could not survive in a pond ecosystem are monkeys, ants, and birds.
An outdoor pond is appropriate for a terrapin because it is a suitable habitat for them. Terrapins are best suited for shallow ponds that are less then three feet deep.
I can get an outdoor pond by digging on in my back yard. FIrst, dig a large hole, the shape of your pool and its depth. NExt, fill he hole with cement so it can take the shape of your pool. FInally, add water and you have yourself an outdoor pool.
There are many stores that sell outdoor pond cleaning items. One place to look for these items would be your local pet store, or maybe even a pool store.
The pond water must contain high nitrogen levels.
A pond pump helps circulate the water properly. If it is not used, the water would sit still and get slimy. If there are fish in the pond it would help keep the water clean.