Boosting the civilian economy is enormously important. And you will need terraforming tech, preferably ship borne modules, but terraforming installations work just fine.
You want to colonize Luna as early as possible and start terraforming it, in order to get the civilian economy producing infrastructure. Once the population is over 25 million, you can keep the population sloshing back and forth between Earth and Luna, (collecting wealth each time), which encourages the civilians to build more colony ships and freighters.
You will want Sorium Harvester tech (after the first couple rounds of economic techs), so you can get the civilians providing fuel for you. Every industry that you can pawn on the civilians allows you that much more growth.
Build a Mass Driver and Civilian Shipyard as soon as you have converted your economy to TN industry, to get the civilians started on building mining colonies. Ultimately, you want the civilians to be handling a significant portion of your mining expansion, almost all of your colonist transport needs, your fuel needs, and much of your freighter needs.
Sector Command is an underrated economic growth tech. As your civilian administrators improve, the Sector Command provides a bonus easily greater than a mining or construction tech, and it is therefore a good idea to get it after the 10k tier of economic expansion techs.