Thanks Igor, esp. on my question about the non-Pro version of PTE AV Studio 10.
Regarding the lengthy time taken to generate a .MP4 executable, I soon realized what the problem was in my case -- since my slideshow was set up to be driven manually by mouse-clicks, I'd left the duration of each slide at 30 minutes, which for 30 slides would mean a 15-hour show. Oops! Knocking it down to just a few seconds enabled the .MP4 file to be generated in less than 3 minutes, as expected given 1 minute of show = 1 minute of rendering.
Thanks for all your help!