Yes, you can. Although I recommend only 2 layers, I have seen up to 4. Make sure the first layer that you are installing over is free of air bubbles and the proper cement is used when applying the new layer.
You have to strip the old one - you need to have a rough surface.
Yes, absolutely! But your flooring contractor will first need to apply a skim coat of embossing leveler over your existing linoleum. This will prevent the old linoleum’s texture from showing through over time.
People do it all the time but it’s always best to lay it directly on your subfloor.
Yes you can to save money but you will need to roughen up the old linoleom a bit so the glue has something to grip to when you lay the new on top.