Sacred Haven of Debauchery

If you engage in warfare, there are no resources for colonies in the early game, and in the mid-game, there is no space left.

Regarding this. There is a tactic for early warfare, but it's quite specific, and I haven't personally tested it (I don't really like that playstyle). You need to play as a militaristic empire (and take the trait that gives a bonus to firing speed) and optimize your empire for mineral production. No colonizer ships; instead, strengthen your fleet. And keep an eye on your neighbors and the size of their fleet. If you see that a neighbor has just colonized a planet, but their fleet is weaker than yours (which is quite likely), declare war on them and demand that they give you their capital. The victory points from capturing a new colony should be enough for the AI to agree to these demands. Well, after gaining control of another large and sufficiently developed planet for this stage of the game, you build up your fleet and look for the next victim.