RE: after being a hardened criminal to start.
19 YEARS FOR A LOAF OF BREAD !! I wonder how many years a few crumbs would be worth...
And it was those 19 years that made him a hardened criminal, not the other way around. Apologies if I wasn't clear on that. He robs the street urchin (a petty, but damning, in terms of timing, theft) after robbing the bishop (IIRC) -- it is upon being caught for with the bishop's silver that he is offered the chance at redemption.
If you are turning the book into a movie or play, it has to center on Valjean. He is the thread that ties the various pieces of the story together, and through them, his path to redemption, self-sacrifice, and righteousness is played. Because of the nature of the medium and time constraints, other parts of the story must be simplified -- so the stage musical (and now movie) centers on this road to redemption and the other players fleshed out only to the point that tells that tale.
Upthread, someone discussed that this would be better material for an opera than a musical, but Les Miserables blurs that line. The vocal and arranging style is musical theater, but it is through-sung and staged in an operatic fashion.