Train as many SCV units as you can, then build at least 5-6 Supply Depots. Continue to train SCV units until you have around 20-30 of them. They will harvest the crystals at a good pace. Build a Refinery and command 2 other SCV's to harvest the ore. Then build a Barracks and an Engineering Bay. Train 10-20 men and they should be able to defend the entrance to the base. Upgrade whenever you have the crystals and the vespene gas to spare. Build Missile Turrents all around the perimeter of your base while you build an Academy, a Factory, a Starport, an Armory, and a Sience Facility.
Once you have the Factory built, train 2-4 Goliath's to help defend to entrance. Now you can build all the add ons. (E.G.) The Comsat Station and the Nuclear Silo for the Command Center; the Machine Shop for the Factory; the Control Tower for the Starport; and the Physics Lab along with the Covert Ops add on for the Science Facility. Now build 8-12 Siege Tanks and upgrade the Siege ability in the Machine Shop. Remember to keep upgrading. Put 4 Siege tanks (in Siege mode) at the entrance of your base and put 4 Goliaths in front of the Siege Tanks. If done correctly, your base will be impenetrable by the enemy forces.
If you are still paranoid that it's not enough, then you can build Bunkers in front of them. If you run out of money then you can take up to 8 Siege Tanks along with 4 Goliaths with an SCV to hunt for more crystals. If you spot the enemy immediately go into Siege mode. The offensive attack on the enemy should be the same way. If you fight the mission the same way, you shouldn't lose that many men! Remember to use the Siege Tanks as guards when out of the base and remember to build Supply Depots when needed.
