i MADE MINE WITH 150 & 300 GAL RUBBERMAID TANKS {arrggh sorry about those caps}
We dug them about half way into the ground and used sections of an old telephone pole to make a raised retaining wall around them. I laid flat rock around the perimeter on the larger one and back filled with sand.
I made a made a whiskey barrel bio filter that spills over the edge making a water fall into the pond.

I started my pond adventures with just a 30 gal planter on the patio with a fountain head and pretty rocks.
Then got a preformed 50 gal liner and then moved up to the the tanks and my self built bio filter/water fall.

when the weather gets into freezing here I just leave the pumps running 24/7 to keep a hole open so the gasses can escape. If it does get solid i just go out and open it up a couple time a day.
We usually only have a few days below freezing at a time, so extreme freezing temps or extended freezes aren't a problem here.

The fish go into a hibernation mode so they should be OK as long as there is an open hole.

I usually just do a major clean up 2x a year {spring & fall} to get the leaves and tree needles out of the water.

Don't let it stress you out -water features are supposed to be relaxing & enjoyable.