As regards the intentions of the show, IMO it can't really be about the life and times of Saul Goodman as we knew him in BB. We've already seen that and it would either have to take on an episodic nature (a new zany case every week) and/or be entirely overblown and far fetched with regards the hijinks of Saul, who we know comes to no harm. Whilst that might be what some expected or wanted it would soon become boring because it provides zero scope for growth or progression. Saul's appearances in BB are usually both scarce and fleeting for a reason, it would be quite tiresome to watch that sort of thing for more than a few episodes and he rarely does more than sit at a desk and offer advice or provide comic relief.
It is impossible to drive the BCS script through jeopardy, as BB did so well, and we are stuck with a reasonably narrow band of characters around which all events must orbit (obviously the writers had a choice in this aspect).
To me, the only way they could ever run the show for more than a season or two is to be focussed on the journey of Jimmy becoming Saul and gradually losing/discarding the aspects of his life that tie him to any sense of normalized morality. As he loses each one of these tethers he lurches closer towards the lawyer we all know. Kim and Chuck have been set up as the two main restraining factors in terms of his behaviour and it will no doubt be the loss of these two that finally releases/propels him to his final resting place on the shady side of the law. Once that happens the show will be pretty much at an end unless it jumps beyond the BB timeline.
We obviously have the parallel journey of Mike (from reluctant ex-cop to cartel enforcer) but the same limitations exist for him. We know when he dies, that he only really cares for his grand-daughter and would rather have a quiet, no hassle kind of life if possible. Straying from these things too far would completely compromise the character laid out in BB and any scenes that allude to peril are reasonably pointless in the scheme of things.
For all the thrills, death and drama of BB it still remained a show based around the idea of what could drive a reasonably meek man to such extraordinary lengths. The Grey Matter angle that is often referenced, the cancer, the repressed ego and feeling of under-appreciation/inadequacy from working in a high school, desperation to provide for his family and the more basic emotions of envy and greed. This is what provided the structure, context and texture to the show and without which the more entertaining bits would have lacked meaning and investment. BCS is doing something similar in trying to establish why Saul becomes who he does but doesn't have the scope for the excitement and carnage that BB did. I actually think it is incredibly similar in many ways but BB had Walt to bring the chaos and change the tempo (which was quite often as slow as BCS).
I'm not saying BCS is fantastic TV, it has it's merits but is somewhat over indulgent at times (it smacks of the creators having been given almost unlimited freedom after the BB homerun), but I do feel it is only ever going to suffer from it's links to BB. BB catered to the more discerning viewer, those who watch soaps and like something dramatic dripping out of every orifice between each add break and pretty much everyone in between. It was rare TV gold that due to it's broad appeal captured more attention and bigger audiences than series of greater craft. BCS can never be that, it would fail if it tried for some of the reasons outlined above.