In an older version of Stellaris, a cheesy strategy is to abduct or force relocate the entire galaxy onto a single planet.
Usually having an overcrowded planet, has a several drawbacks.
Since you can never generate enough food, your population will always be in decline. But this decline is capped per planet, and is quite small. As long as you can keep abducting and force relocating pops from your conquests, you can grow.
Similarly, you ignore consumer goods for the only cost of a reduction in produced goods from jobs. But you barely produce anything via jobs anyway.
The low happyness and overcrowding causes stability issues on the planet. But again, the negative stability is capped, so you enable martial law on the planet, and build fortresses, which provide a stability boost per soldier job they create. And only stability matters for revolts.
You need minerals, but you can get those from mining asteroids.
Your energy credits come from being a mega church, in which each pop following your religion, generates some credits, along with trade generated per pop.
Alloys come from turning the planet into an ecumenopolis. Although you get a -50% production modifier, it is the only thing you need to produce yourself.
But the real trick is giving all the cramped up pops utopian living standards. In this version of Stellaris, any unemployed pop living in utopian living standards, generated science points and trade value. Usually those are barely worth the extra cost of letting the pop live so luxuriously. But even if you don't provide food and consumer goods, they still provide sciencd and trade.
As a result, you got a stable planet generating insane amounts of science, energy credits, and alloys. While remaining a small empire, which kept tech costs low.
