Adding a still image at the start of a video

[sark]

You probably don't want the image to fly past the eye of the viewer within a tiny fraction of a second

Yes, I was taking that for granted. Should have included the Still image filter in the above steps.

you need to generate a video from the image, a video with a matching audio track. Choose a lossless codec for that. Then append it to the original video and perform whatever editing steps (copypasting, deleting, filtering) you need. Re-encode the whole thing.

I see where you are coming from, because once the image video is appended (with audio) you can paste the cut end section back in, complete with its audio.
The only minor issue is, the image will be encoded twice, hence my approach. However, with an intermediate lossless codec this shouldn't be detrimental, and as you say, it's more flexible.