You have 500,000 population each hab blocks gives living room for 5,000
[ ] Defunct Imperial colony: The dead imperial colony could be restored and expended with minimal effort as its curtain wall is only breached at 24 different locations (50 preexisting hab blocks, 1 preexisting small plasma reactor, -100,000 metal, -50,000 promethium)
[ ] Omnissiah falls: These are the largest set of waterfalls on the planet with an untold quantity of water falling from them every second. It is far out of your reach but one day these falls could be turned into a powerful powerplant outputting more power than a hundred plasma reactors. (unlocked hydropower project, -at least 1 colony ship, -100,000 metal, -50,000 promethium, +50 hab blocks)
[ ] The southern steppes: As far as you can tell this is the safest place on the planet to establish a colony (-at least 1 colony ship, -50,000 metal, -25,000 promethium, +50 hab blocks)
[] The frigid North: This colony site sits onto of an ocean of promethium. (50% cost to establish 20 promethium fields, -at least 1 colony ship, -100,000 metal, -50,000 promethium , +50 hab blocks)
[ ] Volcano: This colony site sits near the largest volcano on the world. While you don't have the STC for geothermal power plants currently you could perhaps build your own. (Unlocks Geothermal power research, -at least 1 colony ship, -100,000 metal, -50,000 promethium , +50 hab blocks,
(all colony cites can be expanded to hold more population by doubling the cost)