I'm not generally a fan of the cliche "every planet has one type of distinguishing feature, be it climate or city or whatever", despite how often it's used. The scientist in me wails about how unrealistic it is, but I see how it's so damn practical.

That being said, establishing a large scope allows for the choice of making it a series of brief stops at a few cities on series of planets, or developing them more. Like you said, otherwise you run out of planets.

I'm not sure exactly how much exploration of lots of worlds in-depth there needs to be, if the player characters are specifically designed to be "space pirates", meaning they spend most of their time in space and not on land.