Christian, there are some really fascinating speculations around the questions you ask (as others note, most of them are not really concerned with big bang theory).

The smoothness problem, the unevenness of the distribution of matter in the universe, is understood: quantum fluctuations in energy density, which are as far as we can tell completely unavoidable, provided the initial irregularities. What I find fascinating is that the size and 'spectrum' of these irregularities, as recorded some 300,000 years after the bang by the cosmic background radiation, matches the theoretical prediction for what these quantum fluctuations should look like.

As someone else mentioned, the total mass/energy of the universe may well be precisely zero: the birth of the universe may have not required anything but a momentary hiccup in no-space, no-time. The deal is, the gravitational energy of the universe is understood to be a negative quantity and this negative quantity is suspected to precisely balance the total positive mass/energy of the universe. But although the understanding of the negative and positive nature of mass/energy and gravity is well-accepted, the exact ratio between these quantities in the universe isn't well-defined, I believe. (I could be wrong on that.)

As far as before-the-big-bang, there are several speculations. Perhaps there was something akin to a quantum fluctuation which caused an unimaginably tiny space to fall into an exponentially-expanding state called the false vacuum; perhaps colliding structures in a previously existing multi-dimensional plenum created the bang; perhaps an imploding black hole in another universe created the initial spacetime point which created our universe (and perhaps black holes in our universe create new universes which are dimensionally unconnected to ours); or perhaps our universe is a bubble of conventional spacetime in an eternally-existing, exponentially expanding super-universe of false vacuum.

These speculations all have some plausibility when cast in the form of mathematical physics, but there's no hard evidence supporting any of them over the others, I think. What we do have is hard evidence supporting the big bang scenario.