Since you are not going to be monitoring the fish the best place for them is to keep them in the pond.

It seems like you are new to fish keeping, so here's a few tips: First, try the pond forum here. It is much more active and they know several different fish, koi in particular.

Next, a new aquarium (or pond, same thing) doesn't have the bacteria to handle the fish waste yet. The first few weeks are critical and you will not be there to handle say an ammonia spike.

Even the worst green water in a pond is actually not a problem for fish. It bothers us much more (as we want to see them!). The only drawback is it can use up oxygen at night (not that Ive ever seen that in my pond) but as long as you have an air bubbler or splashing water from a fall or such it should again be fine.

You don't say where you are in the US but unless it's Alaska the temperature in the pond should again be fine till you get back. Your pond sounds too small to winter over in it so transferring to the tank is best.

My pond is about the same size but here on Long Island NY it only freezes an inch or so and I do winter over fish right in the pond, no heater.

I live in Minnesota and a women I know puts the few Koi, I think 3, in one of those childrens hard plastic pools for the winter. They have survived for the 5 years that she has been doing that. She does run a pump, checks water and does partial water changes, just like a big aquarium.

PLEASE DONT USE ALL CAPS!!! ITS ANNOYING

Yes green water is good for your fish 3 ft of water is plenty for your fish in the water. i live in mass iand my koi do fine in the winter.If u need any help let me know Mark