I dont do more than 3 in a set usually. For whatever reason, only 1 image sells well out of my sets, everything else just has 1-2 sales or nothing at all. Majority of my buyers dont buy more than 1-3 images from me at a time.
I usually upload 1 image and wait if it gets rejected or accepted, then I add more. But its definitely easier to add all 3 images at once and forget about them, move on to a new subject. There is so, so much to do, so many ideas, so little time. I tend to loose my prompts in the amount of folders that I have on my discord server.