OK here's my real recommendations for expansion:
1. Build some basic missile defense PDCs and ships with your starting tech.
2. Explore the nearby systems with jump-capable GEVs and GSVs.
3. Drop some infrastructure on Luna to get your civilian shipping lines up and running. They will take it from there.
4. Build 2 civ shipyards and expand them out to 100-150kT capacity, then add slipways. One is for a huge terraforming platform, the other for a huge fuel harvesting platform.
5. Build more civ shipyards to produce tugboats for hauling those platforms into place. Drag them to whichever planets in Sol make the most sense, while you build up from 1 platform to a decent sized fleet (20 or so of each is a good stopping point). Then start tugging them to other planets and stars, wherever they can be put to use.
6. Build 3-5 gate construction ships and start building your jumpgate network.
7. Short-term, begin hauling automines to comets, and buy every mineral the civilian complexes mine.
8. Look for terraformable planets with large (millions) deposits (0.8-1.0) of each mineral. Make a long term plan to colonize, terraform, and load them with non-automated mines. Build fast freighters to transport the minerals to Earth. You now have a near-infinite supply network and don't have to worry about comets and asteroids any more.
9. Explore and conquer NPRs until database bogs down too much and you have to start over.