Not the hardest ? I haven't a clue how to do it
At least with my gigantic game, I was able to hide long enough to build a working economy, even though it was puny compared to the AIs. That meant money for bribes, and being able to research techs the AIs did not have (more bribes, and trades with the minors). On tiny maso so far, I haven't found how to prevent the aliens from showing up with comments like :
"Nice little museum you have here. Looks like the best collection of vintage corvettes in the galaxy. But I hear you have financial troubles, I'm sure you'll be happy to donate it, we have an old Dreadnought that will be quite at home here. We'll even keep the name, what was it, Sol, if you want ?"
And they won't take no for an answer