Energy and matter cannot be created or destroyed, but it can be converted to one form or the other..energy into matter or matter into energy, per E=mc^2. But your question relates as to how matter and energy can be created from empty space-time. The answer more or less in non Hawking terms is that 'empty' spacetime consists of equal amounts of both positive and negative energy...that adds up to nothing...but for some inexplicable reason the positive energy has won the battle over the negative energy and converted itself to matter, antimatter, and photons...which is exactly balanced by the remaining negative gravitational energy of spacetime...such that the entire energy in the Universe, when you convert the matter back to its energy equilavent, remains at ...NOTHING. No energy at all!
And yes, time and space are inseparable, at least beyond Planck limits, and outside of the region of the black hole singularity (if it exists), where spacetime and all the laws of Physics break down; and, at the speed of light in a vacuum, where time and space is nought.
And finally, on Dark Matter, while there are many theories, the most promising seems to stem from M-Theory...where Dark matter is actually gravitational energy seeping into our 11 dimensional Universe from matter in ANOTHER universe , via way of black holes!
BTW, some say the separation between the universes is only a few millimeters. I don't know the mathematics behind this, but I would venture to guess that they are much closer than that: 1.6(10^-33)cm, the Planck Length of the unknown. No other distance makes sense.