I just wanted to report that I’ve just completed a third project. This time, it was extremely straightforward. Like the first movie, the audio stream was 48000 Hz 128 bit/s mp3. ffmpeg did not report any errors. I just ran its output through SMC and everything was fine on my Sansa e260v2.
I’m reading more on ffmpeg and it might be possible to optionally expand the WinFF preset command line (and save as additional presets) to correct the types of issues I faced in my first two projects. More later if I’m successful doing this.