Short answers, pulled from the story.
The Latin word Germani appears in Roman records from the 1st century BCE. Its origin remains a subject of intense scholarly dispute with theories ranging from Gaulish sources to Celtic etymology linked to words meaning neighbors or war cries.
Archaeologists associate the earliest clearly identifiable Germanic speaking peoples with the Jastorf culture of central and northern Germany and southern Denmark from the 6th to 1st centuries BCE. This culture existed around the same time that the First Germanic Consonant Shift is theorized to have occurred, leading to recognizably Germanic languages.
Romans withdrew after their shocking defeat at the Battle of the Teutoburg Forest in 9 CE following an ambush by Arminius of the Cherusci that destroyed three legions of Publius Quinctilius Varus. Rome gave up on fully integrating the region into the empire and established state policy to expand no further than the frontier based roughly upon the Rhine and Danube.
The Migration Period is traditionally cited by historians as beginning in 375 CE under the assumption that the appearance of the Huns prompted the Visigoths to seek shelter within the Roman Empire in 376. The end of the migration period is usually set at 568 when the Lombards invaded Italy.
The second of two Merseburg charms mentions six deities: Woden, Balder, Sinthgunt, Sunna, Frija, and Volla. These names appear in Old High German manuscripts dated to the ninth century and correspond to cognates in other Germanic languages such as Old English and Old Norse.
The first Germanic people to convert to Arian Christianity were the Visigoths at the latest in 376 when they entered the Roman Empire. This followed missionary work by both Orthodox Christians and Arians, including Wulfila who was made missionary bishop of the Goths in 341 and translated the Bible into Gothic.