I‘m currently writing a paper on the ethnogenesis of the goths but I‘m taking a pause for today to look at Reddit if there are any people that need my specific expertise :D

My main source is the bibliography of Herwig Wolfram, so if you’re interested in that topic, you may read his works.

I won’t answer your questions bit by bit because there are some basic things that we need to clear up and I can cover more ground if I start answering more broadly and then go into some specifics

To start off, what you have to understand that most of our sources come from the Romans. That is very important! In an oversimplified way they structured the world into: Romans, Greeks and Barbarians. They go into some detail differentiating between specific broad groups like Gauls, Britons, Germans, Scythians etc. And sometimes they go into even more details because of specific circumstances, like Caesar invading „Gaul“ and listing all the different tribes by name or Tacitus listing several Germanic tribes. Here we have to keep in mind though, that they called the tribes by their Roman names and sometimes even bunched together groups of people who may have had more complicated diplomatic relationships. The tribes themselves often didn’t write anything about their own identity so today we call them by their Roman-given names, call their structures „tribes“ and „kingdoms“ which in itself is kind of questionable and probably omit several structures, people, identities, villages and more that the Romans didn’t mention.

Now we get to our second sources next to the Romans: The Barbarian kingdoms. „What ?“ I hear you shout in surprise as I just said that the barbarian tribes didn’t write anything down. But they did, after they became proper kingdoms on Roman grounds. After the fall of the Western Roman Empire in 476 and the establishment of the Ostrogothic kingdom in Italy, the gothic king commissioned a gothic-Roman senator and writer (Cassiodor) to write a gothic history or origin story, called an origo gentis in 520. We don’t have his history anymore but later, in the 550s another writer called Jordanes wrote the Getica, a historical source that deals with the origins of the goths as well. And this one is still available to us. Wolfram eben suggests that Jordanes didn’t change too much from what Cassiodor wrote.

So what’s in it? Well, a lot of questionable stuff and a lot of topoi. What are topoi?

Topoi are basically stereotypes. Something like „all barabarians are big and strong and fight naked, also they are unclean, stutter, are bearded and uncivilised. If you see sweeping statements like this about any people of antiquity, be very critical (here we go back to the fact that most of our sources are Roman and that we still often think about other cultures in the way the Romans wanted people to think about them). But topoi go even deeper than that. They were also concerned with the origins of some cultures and people. The relevant stereotype is that of migration: the migration of Cimbri and Teutons because of climate, not enough food or too many people, the migration of the Helvetii or the Suebi or the Goths and Alemanni and so on. This topoi is very much questioned by historians nowadays though it was accepted for a very long time. Findings suggest that certain people really migrated though the reasons are not very clear. Overpopulation is probably not one of them. Germanic societies had no real surplus production that could sustain a big population and huge birthrates and most definitely had a high child mortality rate. Especially in Scandinavia most tribes were 5 guys sharing a pitchfork (I‘m joking of course) so it’s highly unlikely that huge numbers of people migrated from there. I won’t go much deeper into why Scandinavia was chosen because whole monographs were written about it but there was a certain sense of awe with a land that far away and with men steeled by the cold and being very strong, cold resistant and horny. That stereotype is of course somewhat flattering and implies a strong ancestry, blood purity, a warrior way so of course, when writing their origo gentes several Germanic kingdoms took advantage of having been associated with that trope by the Romans (not only the goths but also the Langobards and several others). This means that our „Germanic sources“ are still very much romanised and romanticised.

Now then; where did the great number of people that suddenly stood at the Roman border come from. Here we get to another problem with our Roman-only sources. They were a bit inconsistent at identifying certain people and that stems from the perspective that the people beyond the limes were kind of irrelevant as long as they took no part in Roman politics. The first mention of the gothic people is most likely when they started raiding the provinces in the 230s AD along the Danube but at that point they were still called „Scythians“ by the Romans, a name that was vaguely given to people living east -ish of Dacia, north of the Black Sea and Caucasus. The first actual mention of the goths by name (after continued raids during the crisis of the third century, and even the murder of emperor Decius in battle in 251) is Claudius II. who beat the Goths in battle and gave himself the title of Gothicus.

So now I have cleared up several points with several implication

1. The Goths first appear around the early 3rd century AD in the provinces around the Danube

2. The Romans did not recognise them as „Goths“ for some decades

3. The Romans made use of several stereotypes to identify the people beyond their borders

4. By the 6th century the Goths has established an identity for themselves, an origin story and used several Roman stereotypes for some legitimacy which are very likely untrue

5. implaction a) there was a process along the Roman Limes of Germanic tribes gaining strength and numbers to start raiding into Roman territory in the 3rd century AD

Implaction b) There was a process of gaining an identity and usage of Roman stereotypes between the 3rd century and the 6th century AD

Answer will be continued...