@Pig Of The Hut, Pig your getting advice from everywhere, I scanned through most of the replies. JTB123 hit on a lot of things.
Just make sure that your friend has built some PC's before, really the only thing you haft to worry about is grounding the motherboard to the case. Then usually the only obvious plug in for fans is the CPU cooler slot. Everything else is really obvious, like the way the CPU goes in. If your having too much trouble putting the CPU cooler on that is because you probably need to extend the bolts out on the arms. You don't need watercooling, just get a $30 - $40 Coolermaster CPU cooler. If I am talking to someone that cares how much money they spend, this is my advice.
RAM: I would get the 1866+ personally, its the new stuff, its out their, 1600 is fast but might as well get the new stuff. The timing it looks like on all the new RAM worth mentioning on newegg is fine.
CPU: Like JTB123 said, the performance difference between the i5's, like a i5 2500k sandy bridge in comparison to the new i7's is not a lot. You definitely want to go with Intel though. You can't go AMD to do what your wanting to do, but that is opinionated.
GPU: OK you want to play and record gameplay that looks good, right? Of course, well you want the most optimal performance as well while you play. If your recording with FRAPS, your recording raw footage. OBS, even setup correctly will not record like FRAPS. OBS, again setup correctly with twitch.tv is fine for streaming. With FRAPS if you set it to record 30 fps video, you can actually be playing while its recording your gameplay at 60 fps.
Then, you take a open source software like, say Handbrake, and compress the raw video from FRAPS down to save space on your hardrive. With OBS you could record for days without filling a 1TB. With FRAPS, not so much.
The point, it doesn't matter what recording software you use, buy a good GPU, your processor is almost just as important because they work off eachother. For what YOU are wanting to do, from what I am understanding from your original post. You need to buy a GTX 970, I would buy this card, its even cheaper then when I bought it.
http://www.amazon.com/Gigabyte-GeForce-Gaming-GDDR5-Graphics/dp/B00NH5T1MS/ref=sr_1_1?ie=UTF8&qid=1428452458&sr=8-1&keywords=gigabyte gtx 970
You don't haft to buy that card ^, but my advice, my opinion, is to buy a good card. That card is great for the money, the 3 fans, the backplate. Its a nice card, I paid $370 for mine, its even cheaper now.
HARDRIVE:
All you need is a 128gb SSD for your boot up like JTB123 said. However, I know your ONLY playing MKX, trust me I understand that. Unless you want to pay for a 500gb SSD, get a 1TB HDD. Now, don't get me wrong here, you could do two 128gb SSD's, for one game, sure. But I would recommend a 128gb SSD for your OS, and boot, then a 1TB HDD. Its what I have, and I promise you it is fast.
Far as Youtube Art/Intros: If you want Youtube Channel Art, and a intro done I know a guy that is really fair. I told him exactly what I wanted, while a simple idea, he did it exactly the way I wanted it. This is artwork, and a intro he did for one of my channels. The last video uploaded under Videos has the intro.
https://www.youtube.com/user/MKSaibot
Russell Westbrook