the size would not be an issue, as if all the matter in the verse was part of the black whole in essance there would be no universe except for the black hole, the immense gravity would take it back to a form just before or at the big bang depending on what thoery. so it would be so small it would not exist or it would be infinate in suze as its is the universe, not the best answer but hey

I have calculated the schwartzchild radius to be 10^15 light years, based on an estimate of 1.6*10^60 kg mass of the universe. this seems to me to be a vast size; over 2 million times the size of the observable universe!!

And since nothing can escape a black hole, not even light, how did the universe grow bigger than this? And since the laws of physics break down inside a black hole, how has the behaviour of the universe been extrapolated back to earlier, denser states?

You're right that nothing can escape a black hole, but this did not affect the growth of the universe.  Your question suggests that you are assuming there was a lot of matter packed into a small space during some point in the universe's history.  This isn't the case - when the Big Bang occurred, there was a lot of energy released, but matter condensed out of some of this energy.  The laws of physics were different at this early time than they are today - or rather, at the energies that existed in the young universe, the laws of physics acted in ways that are difficult to observe today. 

It is generally accepted that following the Big Bang, the universe experienced Inflation.  This was caused by the energies unleashed by the BB being repulsive, like magnets.  Inflation was a rapid growth in the size of space, expanding much faster than the speed of light (speed of light is the speed limit within space, it doesn't apply to speed space itself can expand at).

The expansion rate of space was much greater than the rate a black hole could have formed at, for instance.  So, any bits of matter that were close enough and dense enough to start to form a black hole suddenly found themselves spread across a much wider distance - they were no longer dense enough to form a black hole. Any black hole that had started to form would have been ripped apart by the expansion rate of space.

Consequently, the breakdown of physical laws within a black hole didn't need to be considered when extrapolating the earlier states of the universe.

It is not quite right that nothing can escape a black hole. Hawking has postulated that particles of negative mass (formed from quantum fluctuations) will be repelled by a black hole while the companion positive mass particle gets sucked into a black hole.

In any case as the blackhole is 'fed' it gets heavier and heavier therefore exerting more graviational force and thereby shrinking the size of the black hole. There is a point where the black hole explodes but I can't recall how and why.

Black holes grow larger as they 'suck' in matter. If a black hole sucked up all the matter in the universe it would reach a huge size, I do not know the exact factor but i would estimate the actual size to be at least as small as our sun if not a lot larger than our solar system, I will research some data to give an approxiamte size, though for a black hole with such mass there may be special cases where the compression of matter becomes even greater reducing the factor of conversion of volume.

Secondly in the short time after the big bang there was no mass, therefore no graviational forces keepinjg the universe together, preventing the universe from simply colapsing in upon itself.