What is the recommended level for the Mothership Zeta dlc quest?
I've done it out the vault, but obviously levelled up a few times making my way to the crash site. The key for me at low levels is using the alien weoponry against them - though this does work well at any level I found, even at 30.
If you want some extra 'security' then try doing operation anchorage straight out the vault, get the chinese stealth armor and you'll be sneak critical shooting your way through the aliens with no problems.
Without spoiling too much, it might be an idea to arange or lead your crewmates into dangerous situations to see what kit they have to loot as well
One problem I had at low levels was not being able to repair armor once up there becasue I hadn't built up enough caps in time, and expect to level up a lot, even on easy settings you will get a ton of xp!