Welcome Jb. A couple of thoughts.
Assuming Comanche Texas. The drain pipe sounds good as long as the pipe doesn�t get leaks around it. Seen that issue several times. Also, in a deluge, the BG will be swept into the bigger pond before you are ready.

The well to fill it sounds like a good deal. Due to well water not being oxygenated, you should run the water over some sort of baffles to break it up and add O2. The baffles can be a bunch of rocks.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP Grandpa