Hello Jon! Welcome to dreamviews!

Question 1: There are a lot of people who say that you can stay in a lucid dream for days or weeks (not real time). Now this is pretty debatable as there is a lot of mixed opinions on this topic. It really matters on how well you stabilize the dream and your confidence. But from all the opinions I have seen on this site I think it's safe to say you can be in a lucid dream (dream time) for about a few hours. Or however long your REM cycle is like Mancon said. Check out the links he gave you as I don't want to post the same links twice giving the same answer. But definitely explore how long you can make your Lds last!

Question 2: That topic is a really commonly debated topic, nobody really has the answer to it because there is a lot more to learn about the dream world. I sort of believe in it as I like to keep an open mind, but like Mancon said it hasn't been scientifically proven yet, but definitely go check out that sub forum he linked you if you would like to learn a bit more. I myself have had a non lucid shared dreaming ish experience but I wont go into that. Definitely try it out! There is still so much to learn about the dream world, it's your mind! Explore it!

Question 3: Like Mancon said, lucid dreaming is completely and utterly safe. You are in the same sleep stage as you are in non lucid dreams. But you haven't heard about anyone being trapped in their body in a dream have you? Exactly, there is nothing to fer when it comes to lucid dreaming. Just relax and have fun!

Question 4: Sleep paralysis is only scary if you are scared of it. It can't hurt you and has never hurt anyone so why should you be scared? If you do experience scary things just remind yourself that they are all just in your head and they can't do anything to harm you at all! Just relax and enjoy the WILD! With the dark spirits in SP, they are just figments of your imagination and can't hurt you. Unless you were referring to the paranormal or something, which I don't really know much about...

Pm if you want for any lucid dreaming questions you have. I know quite a bit and can definitely help you out!

Good luck!