Arma 3 Dedicated Home Server

I have been playing the hell out of Arma 3 lately and decided to build my own dedicated server. 
Mind you the current system is slapped together with parts from the boneyard (closet). If I find it to be worth it I will slowly upgrade.

Current Specs:

MB: MSI-7309
CPU: AMD 64bit Athlon II  +5200 Bisbane (2.7ghz)
(I have been beating the shit out of this MB and CPU for years and it won't die) 
HDD: 500G - some sad old Hitachi
RAM: 4G - I beleive out of some old HP Desktop
PSU: Some random 300w
OS: Windows Server 2012 (I've several retail keys being a student and registered with MS Dreamspark and BizSpark)
ISP: The Devil (Time Warner) : 50mbps \ 5mbps
Modem: Arris (Provided by the Devil)
Remote Desktop in order to run it headless

I haven't had many people join the server at once, so I have no clue how it will do under load. (Please note: That is not an invite for a Ddos lol)

Now on to my questions:

I plan on hanging onto the MB \ CPU for a while and make my first upgrades to be an SSD and possibly a NIC. 
I'll be purchasing a couple new SSD for my primary PC and placing the current one into the server.

What NIC would you recommend I go with that will give me an advantage on my current board that will still be usefull when I do upgrade my MB? 

Knowing that no matter what I do, my ISP will end up being my biggest bottle neck, do you have any suggestions on modem settings that will give me the best connection I can possibly get? 

What sort of security precautions should I be looking at?

Is there anything I can do for Ddos protection?
Arma is notorius for getting hit with Ddos.

I can think of tons of other questions, but I will leave it at this for now.
At the time of this posting my server is currently down (OS updates), but if there are any Arma 3 players here you can find my server by placing "B13" into the "Host Filter" . Running 404Wasteland at the moment.

If anyone is interested in setting up their own Arma server I can write up a tutorial. It took quite a bit of searching and reading confusing instructions before I figured out how easy it actually is to setup a headless dedicated server for Arma. 

Also I am working on my own custom MP scenerio and would love it if we could toss some ideas around for me to implement into missions. 

Thank you in advance to those that take the time to read and reply here. 

Sorry for the double post... I don't know what happened to the first post.. I had spaces in there to make it more readable...?!