Sorry for the finger! I use the waterfall with a built in filter. Not sure it’s absolutely necessary the plants and fish are good at it. Frequent top offs and bottom vacuum and beginning and end of season keeps the water clear. I have used some Algae stop in the past and put in a bottle of bacteria each spring. Only feed when temp is consistently above 50. Japanese Koi only and they had babies. I am going to install a Seneye this year since I don’t use it with my reef.
Looks like you have some sound advice. I would only add one more thing. When you dig the pond even if only 1 foot max have a ledge of 6 inches or so all the way around. The ledge serves many purposes not the least of which is aquascaping. The heater ring in winter is key. The fish survive either way and hover at the bottom if it doesn’t freeze all the way down. Mine is deeper than you are planning but I still use the ring to prevent expansion issues from the ice on my perimeter. Have fun the planning and building is the fun part the observation is the relaxing part later. Early morning oatmeal, my glass of OJ and my bone broth protein drink are my go to zen time!!
