It is interesting how much legend has built up around Joseph of Arimathea. It's like the bit that is told about him in the Gospels just whet appetites. His story got expanded in the non-canonical Gospel of Nicodemus and some additional details about him show up in writings of people like Iraeneus and Tertullian. Eventually, of course, he somehow got identified as the first Christian missionary to the British and (even later than that) as the first custodian of the Holy Grail, but none of this predates the Middle Ages and a certain amount of it is Glastonbury abbey in the UK fluffing their own reputation. To be fair, there is evidence that Christianity arrived in Britain quite early in the faith's history, just none that supports Joseph being the one who brought it.
On topic, Joseph's role is interesting in light of some comments from Father Just. He points out that the best models of faith in Mark are generally not the Apostles, who are often questioning, squabbling, and so on. It's minor players like Bartimeus, the Syro-Phoenician woman, the bleeding woman, and such. Joseph kind of fits that mold, too.