Dreaming about plane crashes is very common, even more so if you're scared of flying and you're about to fly soon. As for the other things, you already said you sort of knew about some of it before it all kicked off; usually your subconscious spots things are amiss in your relationships and interactions with other people way before you fully realise them yourself, that's why you often dream about things happening before they do, because your subconscious mind is expecting them to happen, or at least thinking that they might happen.

Pretty much all your dreams are based on what your unconscious mind thinks is going on in your life, sometimes the things you dream about will actually happen, but more often they will not happen - your unconscious tries to guess at everything that could happen, so all its guesses can't be right but because there are so many guesses some of them must be right now and again just by the law of averages if nothing else. Dreams are usually more accurate than averages though because they are based on unconscious guesswork derived from everything you are doing in your life.

Of course your dreams or unconscious don't have any data on the operational status of the plane you're going to fly on (unless you are the pilot or one of its engineers) other than the fact that you are worried about it, so you are shown images of crashes to give you a chance to make sure you are certain you really want to go through with the ordeal.

You have to remember though that your unconscious mind doesn't know what a plane actually is; it doesn't know anything about flying; it only knows that thinking about this particular image frightens you and that you connect the fear of this image of flying with the image of crashing, and that you are intending putting yourself through this trauma sometime soon.

Your unconscious mind just wants you to be happy and safe and never frightened and in danger, so sometimes it shows you things about upcoming events that it knows you are frightened of, to make you think about whether or not you want to do them or not - the unconscious mind is not perfect, it can make you even more anxious sometimes that it intends, and its predictions are often completely wrong. For instance you may be taking an exam sometime soon and be very nervous about it, inevitably you will have an anxiety dream where you fail and some kind of horrible thing happens to you - yet you may go and pass the exam easily because you find the answers are easy. Your unconscious mind had no way of knowing what the answers were going to be, so it had now way of making any accurate predictions any more than you could yourself in waking life - it's the unknown outcomes in life that cause us the most anxiety, where the time leading up to an event is often far more frightening than the actual event itself.