What did the Jews during the First Jewish-Roman War know about other anti-Roman revolts?

One factor to keep in mind is that the Romans had organized most of their eastern provinces south of Asia Minor only starting in 64 BC. Egypt had been formally annexed only in 30 BC. Before that time frame, the political situation in Palestine and Syria had been incredibly fluid all through the time frame of Alexander's successor states and empires. Judea had only been annexed as a province under the emperor Claudius, so in living memory at the time of the revolt Judea had been nominally independent as a client kingdom.

Jewish zealots in the mid 1st century would have had every reason to believe that empires and kingdoms were ephemeral entities that came and went. We have the benefit of hindsight to tell us that Roman (and later Byzantine) rule in this area would be stable for centuries to come, but they didn't have that. Hindsight from their perspective told them that the Ptolemies fell, the Seleucids fell, the dynasty of Herod fell, etc.

I can only give part of an answer. However, Josephus, a moderate Jewish leader of the time who changed sides when he decided the Jews could not win, subsequently wrote a 'History of the Jewish War' and other writings about it. He twice puts into the mouths of Moderate Jewish leaders speeches in which the ask how their people can hope to stand against the Romans, who are so powerful 'they have conquered even Britain at the end of the Earth'. However, they do not mention Boudicca's revolt specifically.

For Mediterranean civilizations at that date Britain was known of as a proverbial 'ends of the Earth' kind of place, rather like 'Outer Mongolia' for us, so for Roman power to stretch from there to Judaea meant they were powerful indeed.

We should not take the 'speeches' in Josephus History as word for word accurate. In a society that valued rhetoric very highly, they were an accepted literary device. The Roman historian Tacitus in 'Agricola' purports to give word for word a speech by a barbarian Chieftain Galgacus to his followers in the unconquered far north of Britain, in which Galgacus appears improbably learned in the techniques and conventions of Roman oratory.

However, even if Josephus made up the speeches, he was himself a Jew from 1st Century Palestine so what he knew and what he thought his readers would find plausible in the mouths of other Jews of the time are, especially in the absence of other evidence, significant.

We know from gravestones and other evidence of e.g. soldiers and others from Syria and North Africa ending up in Roman Britain. Indeed the Romans often posted troops to parts of the Empire distant from their place of origin, so they were less likely to join in a local rebellion. When enslaving war captives there was an advantage in selling them to a distant part of the Empire where they had less chance of escaping back to their own countries. There was also quite a lot of long distance trade within the Empire.

Consequently it was by no means impossible that occasionally someone in First Century Palestine would meet someone from or who had been to Britain or provinces in more direct contact with it such as northern Gaul.

First off, the idea that the First Jewish-Roman war was futile is wrong. The war lasted several years, the Roman armies were defeated a few times. The main reason for failure was Jewish infighting and therefore a lack of cohesion between Jews themselves. "Professional armies" are not magically better than volunteer armies, or even conscript armies, as proven many times in history. It all depends on training, tactics, and willingness to fight.

As for news about similar rebellions and revolts, it is plausible that the inhabitants of Judea did hear about some of them. In those times the main source of news was word of a mouth, with the occasional official proclamation in the public square. Very few people in those times were literate enough to comprehend the true size of the Roman Empire, and the associated strengths and weaknesses of that colossal state. But they did know their local situation, had an idea about the size of the local Roman forces, and of course they had their own worldview which was often based on religion and emotions (we against them) .

Considering that stories like the story of Boudica could be interpreted in various ways, rumors about that event were certainly shaped by views of the storyteller and the listener. Those that were afraid of the Romans might emphasize her eventual defeat and the slaughter of her supporters. Those opposing Romans and willing to fight could downplay their defeat, blame it on treachery or simply ignore it. Instead they could spin it as proof that Romans could be defeated, even by women.

Of course, chances that this particular revolt influenced leaders of the Jewish rebellion in significant ways are minimal. There is no record of anyone of them mentioning it, and realistically Britain was a barbaric land on the far edge of the Empire at that time. Instead, the main motivation for Zealots and others was religious (they didn't want to be ruled by Roman "heathens") and inspiration mainly came from the Jewish holy scripture (later compiled as Old Testament) which did have many examples of Jews defeating stronger forces if Yahweh wished so.