The answer to (3) is - maybe. It depends on the laptop's software. You could try it

But I wouldn't bother, especially as you've never used Powerpoint. My wife does U3A talks with presentations in LibreOffice Impress, which is free. They should have that on the U3A computer. And if not they should install it! And anyone in the group can install it too.

You can insert diagrams and images into slides, in both Powerpoint and Impress. I would avoid anything complex.