There is another way to gain colonies early in the game, here is what I do:
Before begin the game, set the Reasearch bonus to 8 or 10, this will give you a very much boost on researching ability which comes in very handy later on. Upon begining the game, set the research project to Communication Theory, fly around while your project is underway, when it is finished, research Nano electronics, after that, research Stella Catography. With this project, you will be able to identify suitable planets in the galaxy map, which are shown like white dot(unsuitable ones are grey). With the research bonus you have, you should finish all those research in 30~40 turns. Did I metion all those time you should keep on building colony ships? The way I materalised this tactic is that AIs dont use maps to find planets, they just KNOW it.
By doing this, I am able to colonise as much planets as possible in very early stage.
~SDC~