According to the Qur'an, was Moses' sister Miriam (c1450 BCE) also Mary the mother of Jesus (c4 BCE)?

No. They were two women of the same name, Maryam. Maryam, or Miriam, is the name in Semitic languages like Arabic and Hebrew. Mary is the Latin version of the name that is present in the Bible, a name which was not likely used in that area at that time. So this is not a contradiction. Sorry.