Background: Around 600 years ago, the whole world was in conflict.
Outside of Ser, the world was a chaotic and dangerous place. Ser was the only neutral country in a world filled with violence and devastation. There were at least 8 wars going on and nobody had any alliances. All trade was cut off.
The country Ser, led by an aging Empress Ana, said the following:
Let them fight, die, or whatever it is that barbarians do with one another. There is no need to intervene, so long as they do not cross our borders.
Upon her death, her son gained the throne and had a much different stance on the matter. In fact, he declared war upon the entire world:
As of this moment, the Ser Empire will begin to liberate the people in the world burdened by their oppressive governments, who forfeited their right to yield power when they abused it. We will extend our hand in leadership towards these victims and one by one, we will unite all of mankind. This will be the last war.
In a nutshell, they were able to actually conquer the entire world due to their brilliant military strategist. I won't go into detail.
In response to being conquered, about 50 years later a superhuman organization intent on overthrowing the Ser government was created called Res. They almost succeeded.
A new secret organization of superhumans called Rova was created, secretly sponsored by the Ser government to defeat Res. Res was defeated and disbanded, only to keep resurfacing every once in a while.
500 years later, in a world very similar to modern Earth, Rova continues to protect the world from the chaos of Res.
I'm having a hard time figuring out just how big secret organizations such as Res and Rova would be. How big would Res be, considering that its leaders and key figures have been defeated time and time again? How big would Rova be, with the support and finances of the Ser government?
The way the Rova organization works currently in my story: They have a shell organization or organizations that are legitimate on the outside, but most of its members are all part of something bigger. For example, the Rova headquarters is located in the capital city of Ser, in a building that leases office space to some other large organizations.
Specifically, I'm trying to figure out how buildings each organization might own, or how many employees I should decide each organization has. Or how they might get away with staying in the shadows for hundreds of years and yet maintain influence on an international scale.
EDIT Clarification 1: Superhumans are born, not made. They can been seen as similar to mutants from the X-Men/Marvel universe. However, there is also some genetics involved: Normal people tend to produce normal children, and superhumans tend to make superhuman children. But it is also not out of the ordinary for normal people to produce superhumans, or vice versa.
EDIT Clarification 2: Although it is true that rebellions thrive on publicity, Res is keeping themselves secret because they aren't strong enough to take on the entire world by themselves. They need to slowly gain enough members secretly until they believe they can take on the entire world's armies. Their political views simply do not have enough public support to justify coming to the surface - especially with their history of violence.