If you want to go the high tech, hidden state route, try this. The RWR starts a colony project ,say a hundred years or so before Stefan Amaris comes to power.
A research center to work on new technology is set up. They have limited manufacturing capacity to build a small number of whatever new they come up with.
Eventually, several other colonies are added to the group, to furnish the raw materials, food and so forth. A small ship repair yard is added so they can keep their starships running without having to wait for resupply from the main sector.
By the time the Amaris coup comes and the RWR is shut down, the colony sector has grown to 8-12 worlds, maybe 3 -4 million people, all interlinked and used to being mostly on their own. Since they were a state secret, the war basically destroys any records of their existance. Once they realize what has happened, they withdraw into themselves.
Eventually, they establish contact with a trading partner, perhaps the Hanseatic League. They trade some of their older technology for resources, but keep the new stuff for themselves. By the time of the Clan Invasion, their population is over 40 million, and their tech level equal to or greater than the Clans.