The first thing you do is build factories to meet internal demand. Liquor should probably be your first consumer goods factory, but you'll probably want a cement factory first. Try to get a machine parts factory early on as well.
Other than that, it's a question of what you can get the resources to build. Furniture and regular clothes both see a lot of consumption, and wine, glass, and fabric are very reliable as well.. You only really need one lumber mill, but being able to make a good amount of steel is helpful. The Production window will tell you how much of a given good is made in your country, and how much it uses. If you're making more than you use, but your factories don't have unsold merchandise, then you're successfully exporting and are safe to expand those factories.
As for RGO size, don't worry: not being fully staffed is fine. In A House Divided, you get large reductions in RGO size as you get more technology, but Heart of Darkness removes that since there's no upside to reducing the RGO's size.