Your first question is not a “Christian” question. It is not a theological question. I am not sure how it is related to questions about Christianity at all. I think you should take a philosophy class and decide what you think personally about this question. This question hinges on the definition of “something” and the definition of “nothing.” The Bible does not define “something” and the Bible does not define “nothing.” I believe that you will be safe to listen to the experts on this question such as Stephen Hawking, as this is not a “Christian” question. Personally, I believe that space is something, as space is a place where there are electromagnetic fields and in which the spontaneous generation of particles can happen, but, like I said, this is a philosophical, not a theological question, so I will let you think about it yourself.
The answer to the second question is that the Bible does use “creatures” in its poetical passages which could be described as mythological. Leviathan and Behemoth are examples. The Bible has a number of genres, including poetry. Leviathan is only mentioned in such poetic passages, not in biblical history of in doctrinal/theological passages. You will not find Leviathan in Joshua or in Proverbs or in Genesis (unless there was a poem in there somewhere). So, it will be surprising for a person of Western mindset to accept that the Bible does use mythological creatures in its poetical passages, but that is because the Western mindset is different from the Near Eastern way of thinking. To the person of ancient Near Eastern culture, it is not at all surprising that some of the biblical writers use mythical creatures in their poetry to tell us things about God. We can assume that the ancient Jews did not interpret Job as implying the actual, factual existence of Leviathan or Behemoth. They understood their own genres.