The above build is really nice, but obviously at the very edge of your budget, and includes many things you don't really need, but aren't necessarily wastes of money either.
CPU - I would probably swap the i7 down to an i5-4690K. It'll get you practically the same framerates for a good amount less money.
Cooler - Good, but only needed for overclocking.
Motherboard - Good, but if you don't want to get into overclocking, you don't need a Z97 board. A H97 board would be fine.
RAM - It's certainly a good idea for the long term to have 16GB of it, but I don't know of a single game that needs more than 8GB to be playable on current operating systems. Could save £50-60 there; you can always add more RAM later.
SSD - You only mentioned two games that you're interested in, so an MX100 256GB would be easily spacious enough for you.
HDD - Good.
Video card - Good.
Case - a bit cheap for a £1500 build, but workable. Not that important, as long as you don't find it hideous it's fine.
PSU - Good.
I would also change a few of the peripherals, mostly due to personal preferences.
Mouse
I'm not big on Logitech mice for gaming, I'd stick with a Zowie Gear ambidextrous mouse such as FK. Yet I can't know what kind of mouse you like to use or how you grip it. However, judging by the fact that you're new to PC gaming, I'd start with a cheap, simple mouse and work my way up from there as needed. £50 for a mouse is bound to be incredibly wasteful unless you're absolutely sure about what you want. I'd recommend a
Kinzu V3 £35,
Logitech G400s £28, or
Razer Abyssus £35.
Keyboard
I'd pay less for the keyboard, I don't think mechanical switches make much sense for a first time PC gamer. Mechanical switches are a luxury that's only become popular in recent years, but are by no means necessary for a complete experience, and some even prefer the smoother and quieter dome switches.
Corsair Raptor K30 would be a great place to start IMO. Backlit, anti-ghosting, media controls, a few programmable keys. A little bit of everything for a good price.
Monitor
I think a 144hz is a great way to start off, as it ensures smooth, high fidelity motions in fast paced games, something you never see on consoles. A high display refresh rate is one of the things why hardcore PC gamers are loyal to their platform.
Sound system
For 2.1 speakers, those Logitechs are probably just about the best bang for buck you can get. But in FPS gaming, especially if you're at all serious about your performance, you'll want a good pair of headphones. In your case, ARMA is a team based game, so you'll probably want a proper gaming headset. I'm currently using Kingston HyperX Cloud headset, it's excellent value for money. Comes with a detachable microphone, two types of ear buds that you can easily swap around, and they're very comfortable. Sound quality is where I need it to be, not top notch but good enough, especially considering the price. £60 on
Amazon. I used to have Sennheiser PC350 which cost over £100, and frankly these Kingstons are more functional and comfortable, and lose out a tiny bit in sound quality and a bit in microphone quality.