Gateway is a six player map in Sins of a Solar Empire consisting of 2 stars and 49 planets.
Official Description: In the Telos System, a Terran planet called Gateway controls the only jump lane to the star itself, and its resource laden neighboring system, Xi. The faction that controls Gateway controls the future.
The best way to defeat your enemies in this map is simple. Create 5 or so scout vessels and tell them to auto-scan the planets in your current system. While your scouts are combing the system, create the colonization capital ship for your respective race and 10 or so attack frigates. Once your scout ships find Gateway (the planet that has the only phase line to the star in the system) send your small fleet DIRECTLY there and colonize Gateway. Gateway should be free from CPU players until about 15 minutes in depending on the difficulty setting. If it is not free you need to take it out quickly and seize it.
From this point you should research long run phase jumps so you can get to the neighboring system. Keep your fleet on Gateway until you build a couple hangers or a star base (also, assign Gateway as your home planet if you have the spare resources, it allows you to focus all your resources on the planet). Don't worry if your original planet is taken by another race, just use it as a spare source of income or a research base until you get more planets. As you keep defending Gateway with tactical structures send the fleet you used earlier into the neighboring system to take the rest of the planets and extractors (which should be easy as there are only two or three ships per gravity well). If you upgrade the star-base at Gateway to withstand bombardment and build one or two broadcast centers than you should be able to hold Gateway indefinitely barring large scale attack.
After you develop the rest of the planets in the other system than you can finish off the game in one of two ways...
1) If you are TEC you can litter the smaller system with Novalith cannons which will take out enemy colonies and home planets without you ever moving from Gateway.
2) All other races should just send streams of frigates into gateway and send them out to pick off the planets one by one (leaving a star-base behind with bombardment resistance and a repair platform is good before you move your fleet on to the next planet). This method is a bit boring depending on how many players you had on the map. Usually all the other CPUs fell in infighting and weaken one another so they don't put up much of a challenge.