Hello! I saw you mentioned you would prefer not to use ffmpeg for that, but keep in mind the proccess would be a lot faster using ffmpeg. My first idea is to get the list of user images and generate fixed-length clips (4 to 5 seconds, as you specified) then, in the same command line, generate transitions (fade out or overlay) from one image to the other. Using ffmpeg "drawtext" filter, we can write the user name on the top of the input image. I think you would appreciate the result.
Besides, one single command line could generate the video you want.
Also, ffmpeg is portable, which means you can use it in almost any operating system, so I believe this is not a limitation.
Now that I explained a bit about how I would solve this task, let me give you a little background about myself. I'm a computer engineer and have worked as a programmer, database administrator, team leader and systems analyst for more than 12 years. Today, I work mainly as a freelancer and you can check my previous employer's feedback to see I'm very reliable and deliver quality work. All my work is delivered, including all and every source code generated. I also give full support to the code I generated, which avoids you to feel lost in case I'm not around.
A lot of my last work has been video-edition-related, so you won't be disappointed in contacting me for this job.
Please keep in touch and feel free to ask more information.
I'm ready to start right now.
Best wishes,
Alex.