The AI, as far as I know, only takes enemy fleets into consideration when deciding whether to declare war. I believe the power estimate of the UI also ignores starbases. I have come to this conclusion because I've found when I turtle hard and just build static defences rather than a fleet, I often get DoWed by enemies with bigger fleets. Who then sit there and do very little because their fleets while much stronger than my fleets, are not strong enough to overcome my starbases. Or they are, but then I move my meagre fleet into the system they're going to attack and my fleet + my starbase is stronger than their fleet. So then they head home and decide they aren't able to effectively invade and so they just... sit there. And wait until they hit 100 WE and then peace out. It's stupid. The AI should offer white peace if it has decided to give up on its invasion.
As to your other question - it's an engi tech. It's the second in the line of techs that increase housing from city districts. I assume you want it for Arcology Project. Keep an eye out for any techs that increase housing in city districts and grab them as you see them. Off the top of my head it's an Industry tech but I could be wrong about that.