Hi zagacious, welcome to the "what is space" thread. This topic seems to be able to spark new discussions from time to time. Your comments might just be one of those times.If you take a volume of Space and empty it of hydrogen and helium nuclei, perhaps a few atoms or even complete molecules of matter and lots of photons - energetic particles fleeting through, when it’s empty, that volume of Space even if it’s shielded to stop even an 'electron' from getting in to pollute this area of purely empty Space it wouldn't be long surely before it contains nuclei appearing from nowhere?
Given the conditions that you describe, though there may be no possibility that those conditions could actually exist, we have a starting point to explore the idea of two concepts; empty space, and energy from nowhere.
Empty space is the easiest to conceptualize and you have done a good job of presenting the idea of empty space.
Something from nothing is a little harder for me to get a grasp of. Sometimes I hear about spontaneous symmetry breaking which in some theory says that nothing can be split into matter and anti-matter to create energy. When to two come together they annihilate each other and we have nothing again. Presumably, the spontaneous symmetry breaking could be a continuous process, and the annihilation may be delayed by the simple fact that it takes time for the particles and anti-particles to find each other, and during that duration, both matter and anti-matter exist. Parameters of how frequent the symmetry breaking occurs in any give space, the volume of space required for it to occur, and the duration of the particles formed can be defined that would allow matter to form that defies or at least delays the annihilation process. Seemly there is a scenario that would result in an expanding universe like we observe.
Personally I prefer the idea that you can't get energy from nothing. That leads to another concept that has some degree of acceptance. It says that energy cannot be created or destroyed, and on that premise, the energy of the universe has always existed.