All of your questions were the biggest issues for physicists before Richard Feynman.
1. It is not the proper way of asking question. The wave-particle duality itself is not the right theory you must consider with. It is better to go this website and listen the lectures given by Feynman in New Zea land: http://www.vega.org.uk/video/subseries/8. If you can't find answer from his lecture, nobody will help to you.
2. Photon is not the fundamental particle of light. In physics language, there is something called quasi-particle or excitation. This is a convention so it is not like electron or...... For zero mass you have to stick with general theory of relativity.
3.  even wiki answer is already good enough for this question that what people are replying to you.
BTW, I am not a physicist either but there are thousands of unanswered questions in physics even now and any theory at particular era will work until people find another theory better than the previous one.
You can also read the book written by Stephen Hawking (about time) just for fun (if you enjoy it!).