The cycle only ends with your conquest, barbarians!

The infrastructure definitely goes without saying! Roman construction efforts started basically immediately, and would only ramp up with time. Clean water and heterosexual roads!

Taxes would’ve varied wildly since Gaul was made of many different Gallic polities. In the Late Republic, provincial taxation could be very exploitative, especially to new acquisitions, because it was ‘farmed out’ to private collectors. At the same time, it’s widely acknowledged (at least by Roman sources, which are hardly unbiased) that Roman taxation had the near-exclusive purpose of funding the military, which would have defended the provincials’ interests (and also, conveniently, suppressed them if they disagreed too loudly). The Roman Republic derived very little excess income from taxation. There was no massive civil bureaucracy being paid, and even public works projects were generally not paid for by the central government (until the Empire, at which point it is generally the Emperor himself paying for it as a symbol of his MAGNAMINITY).

Civil rights would have depended heavily on what side you took in the Gallic Wars. Those who were consistently rebellious would’ve ended up with their regions as provincials, who effectively lacked any rights except the rights of free people. You would enjoy protection from arbitrary punishment and non-government abuse, but not protection from Roman magistrates going through proper procedure leveling any ‘standard’ punishment they wanted upon you, up to and including death. Anything that could be justified in a vague report to the Senate as upholding public order would have been kosher, as long as it didn’t cause a fuss in the province itself that the Senate (or Emperor) would start asking questions about…

For example, during the Empire, some of the first Christians executed on record were executed for the crime of ’obstinacy’. Their obstinance? Refusing to recant some strange cult when the local governor told them to. Believing wasn’t a crime, but refusing a governor’s orders was!

At the same time, even notably harsh governors recognized that unrest provoked by excessive authoritarianism would mean the end of their careers. Pontius Pilate, of Biblical fame, has a number of his actions recorded by Jewish and provincial sources unfavorably, but even though he’s near-universally scorned for being heavy-handed, he is ALSO often recorded as rescinding and compromising with the locals. Not, one presumes, because he was Harvey Two-Face flipping a coin to decide to be whether a shithead or not, but because even the “LAW AND ORDER” shitheads realize that a riot means answering to the central government why the fuck there’s unrest in YOUR province, and that’s potentially career-ending.

On the upside, the chance of the local Roman magistrate noticing anyone for petty reasons was pretty low, since each official would be handling generally literal hundreds-of-thousands or millions of people. The centralized Roman bureaucracy was small.

On the other hand, those who sided more-or-less with the Romans during the Gallic Wars would have been granted Latin rights, or even Roman citizenship, for their entire polity. Under Latin rights, they would benefit effectively from all but a handful of the protections that Roman citizens themselves enjoyed, and would have a ‘fast-track’ to Roman citizenship as well if they put their minds to it. So if you picked the right side at least half of the time, you could end up in a pretty secure position, with many Gauls reaching high positions in the Empire just two generations later (it could have been sooner, but Augustus was an Italian chauvinist who expelled the Gallic-born Senators that Julius Caesar appointed).