Have you built any agridomes? You need those to feed your people. Also, research Hydroponic Growing Media.
Use the Earthworker to create tubes, concrete walls, (if Plymouth) Lava walls (with research), and (if Eden) Blight walls (with research).
There is no particular order to connect structures. You can connect them any way you wish so longer as it connects to a Command Center.
Make sure you watch your Tokamaks and build another one after you start getting your research and start building more structures.
EDIT: (hope you don't mind me editing your post. I just needed to fix something.)