I don’t have any experience with making mods, but I did use a chunk-editing program once. I flew around in creative until I found an area I liked (kind of a valley, with a huge semicircle of mountains on one side, and ocean on the other). I then used the editor to delete a few hundred chunks in a radius around the circle. My objective was to have a finite area to explore around in, so that my incessant terraforming would have an end point. I don’t know if that’s your objective as well, but it’s an option.

I’d highly recommend Distant Horizons to be able to see the whole thing at all times, without relying on render distance 😎