I was about to start talking about MWO, but then I recognized the name, so I assume you’re asking for specs related specifically to Unreal Engine?
Anyway, to flesh this out a bit - The player number is directly based on how well you want your game to run.
FPS, server/client type, graphics, etc. All affect the amount of players you will have in the game.
The higher your graphical fidelity and complexity, the fewer players you’re going to want to have (cuts down on rendering of player models, and well as processing the actors/actions)
Are you going to have Permanent servers the game will be played on? will the “server” be one of the players?
How are you going to determine who hits who? will the decisions be made client side or server side?
The speed, style, complexity, framework, and overall design can change this.
Graphical scale can also be an issue.
Edit: Ah, went to your website, I see what you’re trying for.