Hello M, I'm building a PC too and thought I could help you out.
For the PSU, let me share with you a rule of thumb:
650W for single GPU, 850W for dual GPU.
750W is surely a great choice and gives you breathing room for OC (Just like xTempered also explained)
I'm not telling you to buy anything, but you could also get
http://pcpartpicker.com/part/evga-power-supply-220g2075... for a bit less. In specs they're the same really.
You could use the extra cash to buy yourself another HDD (or SSD) since you are editing videos. With another HDD you could hook up RAID too. Not telling you to buy anything, just giving you suggestions/ideas.
You could fit your OS and select games into a 128GB SSD, but if you do want more here is an idea.
Buy another SSD and fill it with the games you record along with video editing applications only. Therefore you have one SSD that will be occupied by only the OS (which gives it lots of room to do as it pleases), and one whole SSD for the gaming life. No more having to cramp it into one SSD. Once again, not telling you to buy anything, just giving you suggestions/ideas.
If you want to go with that plan, you might want to save some money so here's an SSD I picked out. (Also for myself)
http://pcpartpicker.com/part/transcend-internal-hard-dr...
I read the reviews on both
Amazon and
Newegg, on both sites buyers said it ran perfect except for those who were unlucky. Still, those are around only a handful. You might want to know though, it is a plastic case. So if you are against that somehow, then obviously this is not the one for you.
Still, you're probably better off with the Samsung, but this is if you want a cheaper second one. If not, go with another Samsung for sure.
If you do go with both of these storage suggestions, you should get RAID and use it as RAID 0 (for performance) or RAID 1 (to backup your precious edited videos and other files) Still, your choice.
Raid levels:
http://en.wikipedia.org/wiki/Raid_0#RAID_0
I know you said you didn't need that much storage so what you could do is set the HDDs for mirroring and back everything up. But obviously you wouldn't get performance. Now if you want performance, go with an HDD like mine (Gaming HDD) which is WD (Well known company) and pair the two as one. With this, you'll get better performance. You could just get two WD HDDs and have an equal amount of storage with the Seagate but since the WD is a gaming HDD, you will squeeze pretty good performance. (Read the link I sent you to understand more) Although you'll get better performance and all, you won't have a backup of everything.
You also said you wanted bang for your buck. The WD is half the storage, but it performs better. The Seagate is twice the Storage and doesn't perform as well. They're the same price. So just get two Seagates and use them in "performance mode." You'll have loads of space and still really good performance. I was just showing you some of the possibilities of what you could do with RAID, I could've kept on going by the way...
WD:
http://www.amazon.com/dp/B00FJRS6FU/?tag=pcpapi-20
For the CPU, you should step up and go with the 4690K (The same as mine). They're almost the same but the 4690K is better.
http://www.pc-specs.com/cpu/comparison-versus/1192/2104...
The difference is not a whole lot but the 4690K performs better and is cheaper. The only con is...4 watts of electricity more.
Lastly, if you want to stream, go for an Ethernet cable. Ethernet cables are the best choice period. But if you don't want a cable running from the router to your PC, you'll have to find a card that suits you well.
Keep in mind:
No matter how good of a card or cable you get, ultimately (for streaming) your stream quality will rely on the upload speed your ISP is giving you. Speed in other things (like watching a Youtube video) mostly relies on your download speed (Although there are a number of things that can affect this. Ex. What time you're watching the video)
How to find your Upload/Download speed:
http://www.speedtest.net/
(Just in case you needed/wanted it)
That's all I could suggest for now
Feel free to check out my build and scavenge parts or do some researching. You could also check out my thread if you want to find out how I got to my build.
I HIGHLY suggest you do research on the parts and this setup before you go out and buy it yourself.
My build:
http://pcpartpicker.com/p/wLrZ99 | My thread:
http://www.tomshardware.com/answers/id-2239287/building...
Hope I helped (: