Animals are clearly conscious in that they observe the world and react to it and even try to proactively manipulate it.
The next level of consciousness, and what most people probably mean when they use the word is human ability to "think in language". That opens up a whole new level, of consciousness, because now we can be conscious of our inner voice. We are conscious of ourselves, apart from the world. Our inner voice can say things about the thing which seems to be the thing uttering the words in our mind. Me.
Is there anything more to consciousness than us being aware that we are conscious? It is truly a wondrous experience which may seem like a hard problem to explain, hence the "Hard Problem of Consciousness", right? But it's not so mysterious if we think of it in terms of being able to use and hear and understand language. Without language our consciousness would be on the level of most animals I assume. Of course it seems that many animals use some kind of language. But, do they hear their "inner voice"? Hard to say. I would guess not.
And so again, in simple terms, what is the question?
The average person may not know the word qualia, but “is your red the same as my red” is a popular question among kids and adults. Seems to be a topic we are all intrinsically curious about. But from a physical point of view, the qualia of red is necessarily some collection of neurons firing in some pattern, highly dependent on the network topology. Knowing this, then the question (as it was originally posed) is immediately meaningless. Mutatis mutandis, same exact argument for consciousness itself.
Evolution just had to give us some way to "feel", to be conscious, about some things causing us pain while other things cause us pleasure. We are conscious of them, and I don't think there's any "hard question" about why we feel them :-)
(1) is perhaps more of a question requiring a strict definition of consciousness in the first place, making it mostly circular. (2) and especially (3) are the most interesting, but they seem part of the easy problem instead. And I’d say we already have indications that the latter option of (4) is true, given your examples from (5) and things like sleep (the most common reason for humans to be unconscious) being in distinct phases with different wake up speed (pun partially intended). And if you assume animals to be conscious, then some sleep with only one hemisphere at a time. Are they equally as conscious during that?
My imaginary timeline of the future has scientific advancements would lead to us noticing what’s different between a person’s brain in their conscious and unconscious states, then somehow generalize it to a more abstract model of cognition decoupled from our biological implementation, and then eventually tackle all your questions from there. But I suspect the person I originally replied to would dismiss them as part of the easy problem instead, i.e. completely useless for tackling the hard problem! As far as I’m concerned, it’s the hard problem that I take issue with, and the one that I claim isn’t real.