I’ve heard that the sleep you get before midnight is of higher “quality” then the sleep you get through the rest of the night, which would mean that it’s important to get to bed before 12 AM - is this true?
I’ve never heard this, but it might be true. Maybe it is insinuating that you sleep better if you go to bed early - because I don’t think the body is on a clock that knows when midnight is. Personally, the more tired I am, the better I sleep, and generally that would be after midnight 
I’m not sure about this however it is true to me that if i go to sleep earlier i am at least 80% more likely to remember dreams better.
I have no idea. I haven’t sleep before 12AM in years (besides some short naps).