How exactly does the Viltrum Empire work? (Mid-season 3 reveal spoiler)

So, around episode 4, Omni-man tells Allen that there is fewer than 50 Viltrumites left in the galaxy. If that's the case, how exactly do they govern? They can't have a Viltrumite stationed on a planet to ensure they follow the path set for them. What does being ruled by a Viltrumite even entail? Do they give tithes? Do the genetically compatible races get used to breed new Viltrumites? If that's the case, there should totally be more than 50 Viltrumites, right? So they're not using the worlds for population growth. I mean yeah I understand they want to rule, but what's their goal? They don't exactly get shit out of ruling rubble and dead men. And they don't seem to be trying to propogate their dying race, since they seem so concerned about Nolan interbreeding with the bug people. I just don't get their goal. Are they just straight evil with nonreal goal?