@SKILORD: I intend to make it clear how to get out of the Classical Age and into other ages. The BTs are just to create the nations that will start seriously fighting in the ITs.
About the Stability/LQ/Happiness, I partially concur. However, there might be a difference between Stability and Happiness. For example, a brutal dictatorship that kept its people in check through torture, massacres and other equally despicable means would be a stable one, since people would not dare to rebel, but it would not be a happy one, meaning that they would probably be perfectly willing to welcome anyone else that comes to free them. That's what happened in Ucrania and Belarus when the Nazis came, but, of course, as soon as they realized the Nazis were worse they mostly sided with the Soviets again.
About research, I am thinking of using a mixed system: having a simple tech tree to signify main investigation, and then allowing the players to develop their own side research projects to get other things, which they would get as long as they can explain how they can do it with their current technology.
I will probably use a tech tree, one derived from the one I used for MilarNES I/II, but simplified to make everything go faster. Of course, I could also do a mix between the tech tree and players' research projects, to make it more interesting. Also, remember that new units' creation will depend on research. So that is another thing to do.
@All others: thanks for your ideas.