First was the Hougyoku being able to destroy the barrier of shinigami and hollows.
He must have met the vizards in when they were shinigamis or they are his subordinates when he was still a captain, or they were shinigami and something happend to them and Urahara help them, or they dont want to be shinigamis anymore, or better yet they are the modified souls that he created that was supposed to be destroyed, Kon is an exception because he got away. Hence knowledge of the Hougyoku.

The points that connect them to him are:
1. There are no other way of destroying the barrier other than the Hougyoku as Aizen said so himself. Thus hollowification is impossible without Hougyoku.
2.There basement looks exactly as Urahara's and he is the only one who can do that because he made it look like the one from soul society.
3. Shinji's knowledge of the Hougyoku.

Also note that Aizen said that Hyougyoku was hidden on Rukias body for a long time. Rukia must have know Urahara long before the series started because Urahara has a shop for shinigami in need in the real world. And this can be proven
when she sees Jinta and said "Your the same as ever shortie". Urahara must've hidden the Hyougyoku without her knowing, maybe from one of those chappy(or rabbit)themed food or cookie things that Rukia cant say no to, or better yet a qiuck heal pill with a chappy image.

And comes the hollowification of Ichigo. The first time Ichigo became shinigami, Rukia gave her powers to Ichigo then maybe giving off powers of Hyougyoku and activating it and destroying the barrier making Ichigo have the ability of being hollowified. Thus also make sense to him having connections to Inoue and Chad's powers, because he have some of the Hyougyoku powers and blended with his raitsu and its spilling out uncontrollably. In Inoues case, her brother must have part of his soul left in the hairpins and because she have deep connections with Ichigo or her purpose got something to do with Ichigo and an encounter with a hollow must have created her powers. In Chad's case, their are like brothers in arms and he made a promise to protect Ichigo(or not) and his purpose for fighting has connections with Ichigo or his motivation has got something to do with him.

And also about Ururu and the others might modified souls if not all must be just Ururu.

I think Urahara has connection to most of the major happenings in Bleach excluding the anime fillers because: he never appeared in shock, always prepared,
his the first to explain things to the others, and also the ability to make portals to other dimensions and knowing whats in there and warning the others about their travels there like he already been there.
And he always comes to the rescue.