We use Amazon's Elastic Cloud Computing (EC2) for our server hosting. I don't know the exact numbers but they have tens of thousands of servers available in each region, and we can add as many of these as we want to our network within a matter of minutes. That's a crazy amount of computing power, right at our fingertips. It's definitely more than we would need for each planet and space station, in every star system, to have their own server.
However, the thing to remember is that having servers tied to specific in-game locations is just a temporary stepping stone on the way to the full server meshing implementation. My guess and my hope is that we'll have left this temporary solution behind by the time new systems start coming online, but I'm not entirely sure how everything lines up on the roadmap, so I might be wrong about that.
The reason we're considering having per location servers as a stepping stone at all, is that it would allow backers to begin testing parts of server meshing before all the other work on it has been completed. To start with, we'd put the boundaries between servers out in deep space so that they could only really be crossed during Quantum Travel. That would really limit, how often players and other entities transition between servers, the kinds of entities that need to transition, as well as what can be happening during a transition. As bugs are fixed and we gain confidence with the technology, we may divide locations between more servers. Ultimately though, the idea is not to have any fixed server boundaries. Instead a server will manage the game for a cluster of players. As the cluster spreads out, the area the server manages will grow, and as the players in a cluster bunch up, the area managed by the server shrinks. When clusters of players belonging to different servers overlap, the servers will decide whether to transition players between them, or even to break out a new cluster of players and spin up another server to handle it. In this version of server meshing, servers will only be assigned to locations where there are players, greatly reducing the number of servers we would otherwise need, and allowing the game to scale to higher player counts much more cheaply.