Masturbation is perfectly normal, but in many families it is taboo. If you focus on it being "bad" it will confuse your own growing sexuality, so understand that nearly everybody masturbates, just some people are more honest about it than others. It is normal to be aroused by pornography, though I'd avoid getting hooked on it because it can become an addiction to the point where some people can't be aroused without it. Since you are so young, I would be careful letting this become a normal everyday part of your routine and maybe just a sometimes thing.
Perfectly normal. You are becoming a man.
I'm 13 too, and masturbation is perfectly normal for our age. Nothing wrong, continue doing what you want to do, just don't masturbate in a prone position.
Sounds pretty normal. Read a book like "What's Going On Down There?" for a balanced perspective on adolescence and all the changes and questions that arise.