Rig for hosting dedicated server - specs help

I'm looking to host a gaming server for simple games such as The Stomping Land, UT 2004/3, Contagion, L4d2, Far Cry 3, Synergy, Sven co-op, Killing Floor, Garrys Mod and Borderlands 2. Basically games that are co-op between 2 to 6 players max. I mainly will be playing with my buddy, so if anything I'd only be playing with one other for co-op style games.

I would be running on a 25Mbps connection, router and a wireless router on the network, obviously I'd have the server wired. Question, is it ok to have a wireless router on the network, as well as having the server wired to it? I would also be gaming on my desktop too.

So here would be the system specs so far..

CPU: AMD Phenom II X6 1090T Black Edition Thuban 3.2GHz
MOBO: msi NF980-G65
GPU: Unknown, required for server? Have a nvidia asus 560 around if that'd work
HD: Unknown on size, depending on OS and how many games. I know I need a fast speed, what would be recommended, for size and speed? SSD may be a bit outta the price range, nothing needs to be blazing fast as it'd just be my buddy and I mainly.
PSU: 550 Watt
RAM: 16GB DDR3 at 1333
OS: Unknown for server type, which would be best for my purpose of server needs? (see below for main needs of this server)

I am really looking to run those dedicated servers where i'd just turn on the rig for when my buddy or buddies want to play, so i WOULDN'T be running this 24/7, literally maybe a couple hours every other day, whenever i'd want to pop up a dedicated server and play with a few friends. I don't have TOO much of a problem on a few of the games to run a dedicated server on my desktop, WHILE playing on the same desktop, but I want to separate it so there'd be less stress on my desktop while gaming.

Any suggestions on any of this? Any help would be great.

Thanks for the help so far. I will for sure grab a graphics card to place in it. But to further clear stuff up, is the mobo and CPU going to be good or decent for what I am looking for, for a dedicated server with maybe max players 10?

Also, can I maybe buy a micro ATX mobo, and use the same CPU? I will for sure be getting a good HD for this.

I have used ubuntu before, but, will most games support the dedicated server for Ubuntu? Would there be a better OS? I have windows server 2003 Standard Edition, as well as windows server 2003 x64 Edition. What are the benefits of different OS's for these dedicated gaming servers?

Also, is it ok if I have a router, with a wireless router in my network, as the server will be wired directly to the wireless router. I will also be gaming from my PC which would also be wired to the wireless router.

Ok, that makes sense. I am going to try Ubuntu Server sometime. I am looking to run video game dedicated servers, but that'll be my job to look and see if I can run those servers through Ubuntu Server. A lot of them run the server in a console, if that helps any if you can give any feedback on that. I think I'll stick with the current mobo I have laying around.

So the wireless router shouldn't matter too much? Maybe I'll test a server on my laptop wired to the wireless router and see how that handles before throwing together a whole machine server and finding out it's inefficient. haha.

Yeah, I figured if I want more players, the better CPU I'd need, but I am looking for little amount of players, very little. Makes sense so far.

Thanks a lot for the help. If anyone else has any input on this or suggestions, that'd be great. I'm going to do some testing on some stuff and see how things turn out :P

It's the WRT610N by Cisco Linksys, it's 802.11N. But at my other place I will be using the RT N66U by Asus.

I am still deciding between Ubuntu Server and Ubuntu Desktop, I know this isn't necessarily the correct website for this, but I am just seeing if anyone has had any experience with that. I am currently trying Ubuntu Server, if that doesn't work I will try the desktop. People say the "guts" are the same, the server just doesn't have the Desktop UI and it's more of just typing in stuff.