Mike your pond is gorgeous and you are fortunate to be able to replace 800 gallons a day. My suggestion is that you wait to add more fish. See if you become addicted to the Koi as many of us Koi keepers do. If you do, you will most likely want to fill the pond with Koi. Also remember to quarantine all new fish before adding to the pond. There are nasty parasite, and KHV. You might want to google KHV as there is a special quarantine that involves making sure the water is heated to bring out the disease. Good luck with your pond. You did very well.