OP,
Just my opinion but questions of origins may implicate time--to our current knowledge time isn't a known parameter outside the universe.
Creation may implicate space and matter--both of which are unknown parameters outside the universe.
Op, your question boils down to how you define God and the scope of his creation.
Let's assume that the consensus theories regarding the origins of the universe and the nature of space-time are generally accurate and correct (i.e. won't be overturned completely). The Big Bang is an accurate cosmology and General Relativity is accurate description of space-time.
If God created the universe, and thus spacetime, attempting to ask questions about features fundamental to spacetime don't follow. It would first have to be established that these features are laws that govern outside our universe and we don't know that.
It is akin to sending a blind email online, "When did you stop beating your wife?" only to discover your email went to a 3 month old female octopus at the local aquarium. The octopus is female (doesn't have a wife), not mature enough to mate, knows not of civil institutions such as marriage, imposes a concept poorly conceived for the species (beating), and altogether assumes the octopus was doing such an act to begin with. Your questions in the OP assume a lot of features familiar to humans would be shared concepts with a being outside the universe. You would first need to establish they are relevant and second how they are defined.
If science is correct about spacetime and cosmic origins then asking a being who "caused" the Big Bang and thus created spacetime questions confined by properties of the universe doesn't make sense to me. How are you defining origins? How could there be something "before" something else if time doesn't apply? Origins itself assume substance which also wouldn't be appropriate. Heck, if there is a big crunch and rebounding Big Bang the universe may emerge with completely different physics so asking questions dependent on this universe's current model or spacetime and how it relates to a being outside such seems to assume a lot about how we define words like origins.
Try as I may I find it difficult to formulate questions regarding "being" and "substance" of any being who could create the universe. Time and substance questions sound childish; questions like "are there others/things" imposes assumptions in how we define finite individuals and objects. Asking whether he has the power to "sustain" the universe ignores the laws of thermodynamics that conclude that from the conception of the universe it has all it needs to be sustained. It is very difficult to relate personally to the philosophical concept of a being who could look at the universe, including time, as (using a human analogy) is nothing more than a marble that is small in the hand and easily manipulated and yet for humans we are confined to the river of time and cannot fathom the size of the universe, let alone something outside it and its laws and concepts. The fact I have to fall back on a human analogy is due to the fact we have no way to relate to such a being on a philosophical basis and questions, based on the concepts of this universe, about the being's nature assume a lot we don't know. We are superimposing our limitations onto that being assumes a lot IMO.
Just my opinion.