...am I aware that this is a war of conquest and not, as Caesar has said, a preemptive attack on ruthless barbarian hordes bent on destroying Rome? Am I aware that I am a pawn in Caesar's greater political scheme to rule the republic? Do I care?
...do we know what we are doing? Are we just going to walk into Gaul and fight everyone we meet? What is the strategy here? Do I know the strategy or is that above my pay grade?
...who are all these people following our legion who aren't roman legionnaires?
...what do I expect is my likelihood of surviving this campaign against savage barbarian tribes? If I do, how will I be rewarded/compensated?
So just a little bit of backstory. Caesar was the Governer of Cisalpine and Transalpine Gaul which is today northern Italy and parts of Southern France. Each territory had a certain number of Legions that a governer would have under his command(which caesar would disregard by raising more Legions than he was legally allowed to raise). But Governers were legally immune while in office so the senate could do nothing about it.
To the first question, an average roman legionary would probably know that in some way they would be fighting in some way which was good for the average soldier. Part of the way that they made money was by sacking towns and basically stealing valuables from conquered territory. The Legionaries probably knew that they were in some part a pawn in Caesars political schemes but Caesar was able to inspire fierce loyalty in his troops so they probably didnt care. They just wanted to fight and make money.
To the second, The Romans very rarely ever just declared war and invaded territory. Usually what happened was that they would look for any excuse to declare war no matter how flimsy. For example, the Second Punic war with Hannibal started over Hannibal attacking a single city in northern Spain. So Caesar would be looking for an excuse to declare war and he got it in 58 BC when a Gallic tribe the Helvetii were planning a mass migration that was going to pass dangerously close to Transalpine Gaul. He had his excuse and threatened to fight them is they didnt turn back, which of course they didnt. So he fought a battle with them and won. The next year an allied tribe called the Aedui were threatened by some other tribes and so he defended them. This is basically what he did every year but the average Legionary would have no idea of the bigger strategy. The only people besides Caesar would be his officers such as his Legates(who would sometimes command single legions by themselves).
The people who were following the Legion could be any number of people. First, they had the baggage train with various supplies and essentials. They carried food and extra equipment for the legions. Next could be the Auxiliary, or the non-roman troops that fought with the legions. When Rome conquered a city or town they would demand troops to fight with the Romans. Almost all of Romes cavalry and skirmisher troops at this time came from the auxiliary and Rome supplied most of the Heavy infantry.
The likelihood of surviving is actually decently good. In ancient battles the vast majority of casualties occured after an army routed and ran. The winning side of a battle usually sustained anywhere from 1-5% casualties and the losing side usually lost anywhere from 30% to being completely destroyed. So if you had a good commander(which caesar was) and won all of your battles then your chance of surviving was pretty good. At this point, when a Roman joined the Legions they joined for a period of 20 years and if they served for all twenty years and survived they would be given a parcel of land. One of caesar's biggest issues after his civil war was to find land to settle his veterans on. Even the auxiliary fought for Rome for a period of twenty years at the end of which the soldier would get Roman citizenship and all subsequent generations of their family would have it as well
Am I aware that I am a pawn in Caesar's greater political scheme to rule the republic? Do I care?
What political scheme to rule the republic? If Caesar at any time actually planned to seize sole control over the state it was no earlier than the civil war, and probably the thought didn't even occur to him until he had already won the civil war. Caesar was obsessed with increasing his own dignitas, not with ruling the state. If Caesar had intended from 58 onward to use his proconsulship to seize the state he did a terrible job of it, since he only barely managed to escape prosecution several times and ended up getting drawn into a civil war in which he was considered very much the underdog until Pharsalus. The civil war began because Caesar refused to damage his dignitas by lowering himself to accept what he considered to be unjust demands and by the inflexible obsession of his enemies to prosecute him, mostly for his unlawful legislation during his consulship in 59, not because Caesar had any grand scheme from day one of seizing the state. That's not actually all that unusual--magisterial and promagisterial positions were sought by members of the senatorial class to increase their own dignitas and auctoritas. Shackleton Bailey pointed out that with the possible exception of Caesar from around 46 until his death nobody before Augustus really thought realistically about the idea of actually restructuring the state. Caesar's overriding desire was to be number one, but that didn't necessarily mean actual control over the state, it just sort of turned out that way after he defeated his enemies. Whether Caesar while actually fighting the civil war had any such intention is a question for more debate, but in 58? Certainly not. In 58 Caesar was, just like every other provincial promagistrate, out to increase his dignitas and personal wealth. There was nothing unusual about it, except that Caesar was unusually competent at what he did and Gaul was an unusually rich province, with lots of untapped potential. But Caesar's intentions when he set off for Gaul were no different than Pompey's in Asia or even Cicero's in Cilicia