"Tight clusters" is probably best.
Super traits: "Colonizer" (free building upon colonizing). Other is optional, though "Patriotic" is probably best for the long game. For smaller maps get "Double Population upon Colonizing" super trait.
Other traits: Fast +2. Sensors +1. Military production +20%. Growth +20% optional (but useful).
Any tech tree. Thalan is probably best given your low population colonies. Hives is awesome with this strategy because it guarantees 4 extra prod in each colony regardless of population.
Colonize [Edited] nearest planet that grants ideology point. Get Pragmatism 3 free constructor ships.
Step 2: Convert constructor ships to colony ships (takes 1 turn). Move colony ships to capital and load up on some population.
Step 3: Colonize worlds with your 3 new colony ships. Each world will start out with a shipyard thanks to Colonizer.
Step 4: Get Benevolence free colony ship.
Step 5: Colonize your SIXTH!! world by turn 9 or 10. Every world will have a shipyard thanks to "Colonizer."
Step 6: have every colony produce colony ships. They'll have minimal population but it doesn't matter. Key is to colonize planets to get Benevolence level 3 free 5 population upon colonizing. At that point you can just spam colony ships with minimal or zero population indefinitely.
Once you have that the game is effectively won on any difficulty below Suicidal on a map where there are plenty of planets to colonize.