Hey. I'm planning on start a massive multiplayer game and I need to know some basics.

The game supposed to be a simple cards game with not a lot of calculations rather then positions animations.
So this is what I like to know:
For let's say 10000 users playing online, each 2 play their own game.
What kind of server is required ( hardware wise ) for this kind of game?
And can I use UNET current services to implement it? I know it gives me a free server but with limits. Is there a way to pay and get bigger traffic Bandwidth?

Also, The server doesn't supposed to show any visuals, I want most of the calculations to be on the clients if this is possible.