Questions

OK - why not!
This adds interest to your page - it can be image, link, text item etc
For simplicity sake lets use images:
1 One way of doing that is to upload group of images and call them something like example_1, example_2, example_3 etc, then add a script which will display them at random. When you want to change any of the images simply upload one with (exactly) the same name.
2 A variation of the above is a List of image names, which you can re-write whenever you like.
3 Another way of doing that is using a database. A script will select an image at random, according to a criterium (for example, from recent images or from images in a specific Category).
Clicking on the image will then take Visitor to that image.
One difficulty is that images are different sizes and formats - the standard solution to this is to crop and scale the image to square of a certain size.