Establishing a colony at TL8

[Dangerious P. Cats]

I have a campaign idea I was hoping to get get advice from the hive-mind for. The premise of the campaign is that earth is attacked by mysterious aliens and overwhelm within a month or so due to the Alien's superior technology. Before final defeat the Government uses an interplanetary gateway (essentially a stargate) to transport a group of soldiers, academics (scientists, historians, sociologists, etc) and officials along with supplies to a distant planet to establish a colony in the hopes of humanity surviving. What I'm trying to work out is the process of establishing the colony, how long it would take, what is the minimum supplies needed and what sort of populations it could support strait off. After the colony is established there's not going to be any contact from earth but I'm not averse to the colonists using the gateway system to try and find supplies. Any ideas would be welcome.