Cosmos Agents only accept a specific amount of Faction Standing for access.
Cosmos Agents offer 3 to 5 part mission series with Faction standing increase on last mission.
Cosmos Agents can only be completed once in the life of the character.
Failing, declining or letting any mission offer expire may lock out access to other Cosmos Agents.
Cosmos missions are tougher, difficulty for level 1 Cosmos mission is equal to a regular level 2 mission.
Most missions are Security encounters that include search and retrieval for a specific item.
Most mission locations are within static Complexes defended by multiple NPC’s with fast respawn rate.
I suggest researching the Agent’s mission series first and make a list of the required items, then collect those items before actually talking to the Agent. That will allow you to easily complete all missions in that series and collect all the rewards without being pressured for time.
Over the years a lot of 3rd party sites with Cosmos guides have been shut down. Luckily due to ‘The Wayback Machine’ most of those guides can still be accessed. I’ve also posted quite a bit of info in these forums about Cosmos and Faction standings.