thats a lot of digging. 125 cubic feet of dirt. You could always go for the preformed type of ponds (not as much digging) right now Im using a 55 gallon drum (plastic) cut in half to harvest plants. I have a filtration unit on it with mosquito fish and guppies with some driftwood. It doesnt get direct sun light so its the closest thing to a pond I got. If you are interested I could get you a plastic drum and you could cut it yourself.
Just let me know.
thanks
john b