stocking question

[Flower1982]

I have an 80 gallon container pond that i've had set up for at least 7 to 8 years. Right now i've got 2 koi in there. I know they are going to out grow my pond so i'll be moving them to my aunt's pond. Her pond is nice and big and she's already got 3 koi in there already. So my question is, once I move the 2 koi out will my green sunfish do ok in my container pond? Would he be ok outside in the winter? I'd love to keep him inside but since he's getting bigger and will eventually get to big for the 20 gallon tank he's in now I thought it would be better to put him in the container pond. Could I keep anything else in the pond with him or does he need to be the only fish in there? Also how can you tell the sex of a green sunfish?
Here are some pictures of my green sunfish:
http://i48.photobucket.com/albums/f216/birdlover1982/greensunfish3-1.jpg

http://i48.photobucket.com/albums/f216/birdlover1982/greensunfish4-1.jpg

http://i48.photobucket.com/albums/f216/birdlover1982/greensunfish5-1.jpg