From watching the 1st Episode and knowing Breaking Bad story line. Here is my take of the series (By the way, have not watched the 2nd episode yet, been busy lately, not time to watch the telly).
I think he is going to make a pact with the devil knowing the circumstances with his older brother and the law firm. That is how he gets to know Mike, Tuco, Gus and the whole underground. The change of name from Jimmy McGill to Saul Goldman might come from disassociation with his brother (protection/firm legalities/etc...). Keep in mind that he does not know Jessy or Walt, that comes later on the show when Jessie told Walt they need a "Bad Lawyer". Saul told them that "he knows someone, that knows someone, that knows someone" when they were introduced to Gus Fring.
I think the producers will tell the guys to show on cameos. Perhpas, later on the series we might see Walt and Jessie making deals with Saul and the storry carry the part that Saul did that was not shown in Breaking Bad.