The FAQ has some pretty good pointers already.

What I want to get out of this topic is an overview what type of server requirement will a game have.

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To quote yourself, "there is no one answer", and there never will be.

There are no set answers to the components of your template, but I can maybe suggest ways to determine them. It's easy to answer "it depends" for each category, so I will try to offer something a little more insightful.

Type of game might have influence over the packet communication protocol you develop; if the game is realtime, your packet design might be aggressively optimized to minimize bandwidth usage. Conversely, a low-traffic game can be more loosey-goosey with packet design optimization.

Typically, clients will be requesting permission for things, whereas the server will be either responding to permission-requests, or simply updating the state of something as it sees fit. For example, a request from a player to move his avatar comes from a client; the server will respond with either (a) yes, or (b) no; in the case of (a) he will likely also update other clients with the new position of your avatar.

Required connectivity is sort of unclear. More bandwidth is better, obviously, but (briefly) your server will need to be able to sustain, at a base minimum, a per-second send-speed at a rate R dictated by the largest packet byte size S, multiplied by the largest number of hosted clients C, multiplied by a minimum operations-per-second threshold T. For example, where S=100, C=16, T=30, then R=46kB/s.

Required hardware is a mixed bag. Given the required S*C*T from above, the CPU shouldn't choke for particularly complex operations, or hang while managing something else in the OS (for example, a database, or an antivirus program). More importantly, your application should try to take advantage of hardware offerings (multiple processors, or CPU-specific features du jour) , where applicable.

Required OS is determined by what your developers are familiar with targeting, what your technology development stack is compatible with, and what you want to pay for. An environment like Cygwin provides many UNIX-like functionalities on Windows hosts, and likewise environments like WINE offer Windows-like environments on Linux. .NET development is (arguably) more accessible on a Windows host, and languages like C, C++, Java, and PHP are everywhere. Servers should strive to utilize system resources as minimally as possible, hence servers which run in a console (i.e. GUI-less, or headless) could be considered a commonplace design. And in situations where a game-server attempts to be online at all times, it might be installed as a service on the host, available upon startup in the situation where the server must be (or is) rebooted.

Required software depends on the technologies employed in your game server, but minimally you need a communications layer (HTTP, WebSockets, plain-old TCP socket server, UDP server, or something in between like ENet), a database (MySQL, MS-SQL, PostgreSQL, SQLite, Oracle, CouchDB, or a higher-level language-specific data-access library which offers something like ORM) if persistent storage is a concern, and possibly configuration file serialization library (for XML, JSON, INI, or whatever your game server uses).

I hope I've offered food for thought. Looking forward to further discussion.