Can you give me tips about doing decoupage?

I haven’t done it since elementary school. I want to do a picture that I have of my husband, but first I thought I’d do a logo of his favorite car brand as a practice of something simpler. Here are my questions:

1. Should I just use Elmer’s glue watered down? Or, use the fancier special glues for decoupage? If I use Elmer’s, do I use it full strength to stick the papers down? Or, everything is with the watered down glue? What ratio should I use?

2. What should I use as the canvas? I was thinking just a piece of cardboard, but maybe I should use a better material than that? I vaguely remember seeing plate that were decoupaged. I think they were glass.

3. How do I project a photo into the canvas to blow it up? Is there a way to do it without an actual projector?

4. Do I need any special sealer for the final step? Or the glue is enough?

5. If I make a plate will I be able to wash it?