You may well find that your version of PowerPoint is "no longer supported". I am no tech geek, but I do have a Mac, and set up an album of photos in the Mac Photos application, and then set it to run as "Slideshow" - which you can pause and re-start when you want.
I'd be wary of doing anything that you hadn't well rehearsed on the same set of equipment that you plan to use on the occasion, having recently hear that a friend's well-prepared audio-visual talk fell foul of technology not working on the day!