Since Matte answered your other questions...I'll touch on 1.

As far as I know, there haven't really been any reliable experiments done to test how easily some people might learn to lucid dream more than others, and if there is anything different about their brains. I imagine it would be a pretty difficult/expensive experiment to carry out. I also haven't heard of any experiments done on natural lucid dreamers, or any decent hypothesis as to why some are naturals and others are not. So for the moment, let's just assume that anyone can learn to lucid dream.

There's really no reason to think otherwise, most people's brains are hard wired pretty similarly. We all have the same ability to gain consciousness. I assume that natural LDers just have more connections or exercise their brains more in a way to facilitate the activation of certain areas of the brain which are typically not active during dreaming (mostly in the frontal lobe), thereby making them lucid. The good thing about this though, is that when new brain connections are made (if you learn to get lucid once), it is easier to use those connections in the future. The brain "learns" to seizure, so if you have one seizure, you are much more likely to have a second one. I think LDing happens in a similar way.

There are lots and lots of things you can try, and if you are persistent, I'm sure you will be able to learn. Good luck, it's worth the effort!