What do you actually need? This isn't really a production question. This is more of an IT or tech lead question.
Part of your development process should involve stress-testing the machines.
You state that plan on having 5000 users. Did you not test this? Perhaps you did not learn from games like Diablo 3 and Sim City?
If you plan on having 5000 users, you must test your system under that type of load. Either directly test with 5000 virtual machines, or have a way to simulate it as best you can.
1) Most work is in quick processing of data, Some DB interactions, mostly logical processing/validation( server controls core game logic to help protect from hacking)
2) My initial thought is that the Database machine should be get atleast 4x drives, Raid 10 (mirrored/striped),
3) atleast 1 T available space. (projected long term needs)
4) Processor should have fast process switching, minimum single i7, 2.8ghz.
5) The Service host, does not need a lot of hd space, still mirrored, physical HDD should work fine.
6) Plenty of RAM, perhaps 32G, Fast. Processor should be stronger, like a Xeon E5, (not overclocked).
1. These database interactions must be stress tested. As database use increases, so does the risk of deadlocks, livelocks, and resource contention.
2. Why? What numbers do you have that makes you think it needs to be RAID across 4 drives?
3. Why? What numbers do you have that says you need 1TB of space?
4. Why? What numbers show that an i7 is necessary? What numbers show a much cheaper i3 or similar couldn't do the job?
5) Why? What numbers show this?
6) Why? How do you know it is enough? How do you know it is not too much?
I know this area is more business/marketing perspective, but the more technical areas don't really have a section that seems like it would work for the technical hardware needs of release time, and this is a production related question.
I'm not sure how you figure that.
The management team might happen to know what hardware is required for the back-end, but that is not their job. That work is delegated.
Also, in what insane world is the marketing team responsible for the implementation of the critical infrastructure servers?
This is entirely a technical question.