Questions to explore

These pieces are thought provoking and quite mysterious, and leave me with many questions to explore.
Since they are incompleted, we are able to view "mid-procedure" how Michelangelo underwent in his sculpting. What were regular sculpting practices at that time? And did the technique used by Michelangelo differ to the conventional practices? We know about how he understood his art as "freeing" objects from within marble, but was this view of sculpting unique in his time?
Why were these sculptures preserved after Michelangelo's death? Were they seen as being valuable back then, the same way they are today, despite being incompleted? Michelangelo was indeed hugely famous in his life, but I do find it questionable that they would have been valuable enough back then for people to keep safe or collect. Or was is more favourable circumastances that have kept them around for so long? Were they appreciated back then as they are today, or was the context of their value different? Was is just by chance or luck that they have survived?
I am also interested in how religion may have played a role in the patronage and the conception of the pieces. They were purposed for the tomb of a Pope, and so I would assume the original design would have had a major spiritual significance. Despite being commissioned by a religious figure, the fact they were intended to adorn a tomb leaves adequate room for assumptions that they would have had a functional religious purpose. What would those purposes have been?
Related to that is the question of whether or not they were originally intended to be slaves, or if today we have come to know them as the slaves due to the context of the time, the artist, and the form which they were left in. What would they have been if they were completed? And assuming they would have had a spiritual meaning, what could their function have been?
Taking the style of these pieces into account, I am curious about where Michelangelo found his inspiration. As a preliminary guess I would say a Greek or Eastern influence. Where did he find his sculpting inspiration for not only these slaves, but for the rest of his marble pieces?