We can’t technically do unlimited on the scale you are suggesting, because that was too much.
Here, what you are looking at, is probably 50-70 Core worlds, and 30-50 fringe worlds. It gives people enough leeway to have core production, strip mining, and attacking others.
Eventually, technically you could go beyond this roughly every couple weeks/months adding a new capital. However it would take a very very long time to get to 200-300 planets. Even then, you would still be limited by your core worlds and the fleet cap.