Well, now you know that nobody knows for sure just where all the places where Mary lived were, or where the Assumption happened.
As for a “Druid University” – you are probably remembering reading about the Roman armies’ final attack all the Celtic religion human sacrifice stuff – which archeology supports as really having been done in Gaul (today’s France and Belgium) and in Britannia (today’s UK). There was some kind of holy place with tons of Druids and priestesses, called the Isle of Mona or Mon. (That’s today’s Anglesey, off the coast of Wales.) The Romans moved in and pretty much slaughtered everybody. (And I seem to recall there’s some archeological evidence backing that up, too.) This is not to say that the Celtic religions were totally worthless and unphilosophical. They had some very deep ideas, from all one can tell. Unfortunately, one of them was the idea that you should honor the gods by burning people up in wicker frames or killing them in three ways simultaneously and then popping them into a bog for all eternity.
The only religions really banned in the Roman Empire were the Druidic form of Celtic religion, with the human sacrifice; a very nasty fish goddess religion that also got up to human sacrifice; and Christianity, which was of course rumored to get up to human sacrifice, but which was really banned for not worshipping the Genius of the Emperor while not having an out for being really old and reliable, like Judaism.
This didn’t stop people from the 1700’s from theorizing big time that Jesus learned everything from the Druids, because Druids were popular then. Jesus has also supposedly learned everything from Egyptians, Hindu priests, Tibetans, Chinese mystics, Japanese mystics… and probably Eskimos and Sioux, too. (Somehow the Irish restrained themselves. They only theorized that St. Brigid somehow got to Israel and was hired on as Jesus’ wetnurse.)
The whole Joseph of Arimathea thing probably comes from the fact that Cornwall’s tin mines drew traders from the Middle East, and it’s possible that Joseph of Arimathea was one. Of course, this has led to all sorts of what-if legends: What if Jesus shipped out during his younger years? What if Joseph of Arimathea hauled along all the disciples? Etc.
But in point of fact, the only common idea among all the legends is that Joseph of Arimathea built the first church at Glastonbury, which was apparently indeed a very early Christian church; and that he planted the Glastonbury Thorn. That’s about it.
There are also legends that the disciples fled to Gaul, and just about everywhere else.
There probably was some amount of fleeing, but as the Acts of the Apostles shows, it wasn’t all that soon. The big flight of the Church in Jerusalem was when the big Jewish revolt was on; and it doesn’t seem that most people fled any further than to cities just outside Israel’s borders.
On the whole, there’s nothing wrong with wondering about the old legends. But believing every single ramification of the plotlines is a bit problematic.