There is no dissent amongst civilians simply because the Empire is responsible for their continued existence, it's not exactly fear to speak against them nor is it that they can't. The Empire, to the average working citizen is like how we see the stars today.
"You can only see them in a certain light, but they're always there."
Everyone knows the empire exists. But they care about paying bills and feeding their family. Not what the Empire does.
The army serves as the police as well, roughly there is 1 million soldiers to every 10 billion citizens.

However paradise isn't what it always looks like, naturalists are the empires primary concern amongst the population, these people think that artificially fueling existence is wrong, religious elements are also seen as a disturbance.
These are generally the main stokers of the fire of rebellion. But they struggle to villify the Empire and the Emperor himself.
However the ones most likely to rebel are those under the 'Curse' and those who already serve the empire in science or the military. Also members of the aristocracy, power is something everyone strives for, but who's willing to try and take it?

And finally you can decide amongst yourselves sir you know each other prior to the start, this will create some drama.

I hope that answers all of your questions McHaggis?