I have to ask - why have you been tasked with this, are you the person that has linux running at home or something?
If you were actually qualified to do what you have been tasked for - there would be no reason for your post.
I suggest you contact a company to help set up your office with the features you need to be honest.
You might want to reach out to say sc302 - not sure where you located, but I believe the company he works for handles this sort of thing. I would point you to mine - but unless your talking 10 or so million in business over a 3 year period we wouldn't even look at you.
If your in the chicagoland area I would be more than happy to help set you all up.. But sorry your not going to get the details you need from a post in a thread on some tech board.
Now if you had a question between which tape library might be best, or which wireless controller to go with, or the finer points of running say your AD dns on bind vs MS dns, etc. Then thread might get you some info you need.
But your asking for a network design, without 1 piece of info to go with other than say 15 users.. Do you have any sort of budget even? Are you talking thousands or 10's of thousands or actual real money to setup something good?
Or you talking a PC running server OS with a wireless router that supports vpn.. There you go your needs have been met - oh your backup, pickup a external disk and plug it in once a week.. There you go - I can draw that up for you if you want That can support 15 users without much issue. Can be done for pennies!
http://www.amazon.co...icrosever gen 8
There you go connect those - add some disks and you have a smb setup.
edit: Here I drew up your network between plays during the game(s)