How Long will this build last?

If you're looking to overclock and run the 970 in sli (2 gtx 970's) then the 650w psu may or may not be enough. Most recommend around 700-750w for sli. Msi is a brand, it's hard to tell from a website with a few nondescript selections from a pull down menu. Asus, msi, gigabyte, zotac, evga, pny etc all make gtx 970's. Each brand has various versions, the difference might be the type of cooler they put on it at the factory, how much it's been overclocked at the factory. For instance various models come at 1.08ghz, 1.09, 1.11, 1.17, 1.18 etc etc. There are evga, evga superclocked, evga ftw.. Without a better description or more information from the website it's difficult to tell what the differences would be.

Just like trying to figure out what power cables are needed. The superflower golden green has 2 6pin pcie connectors and 2 6+2 pcie connectors. (6+2 can be used as an additional 6 pin or as an 8pin). Some gtx 970's need 1 8pin, others need 2 6pin, some need a 6pin and an 8pin - again it depends on which model. While the golden green appears to have just enough pcie power cables to conform to most mixes of gtx 970 in sli, it still may not have quite enough power. Pushing a power supply to its maximum load rating can put a lot of stress on it and as it ages and weakens how much power it can deliver, there may be power problems down the road. Though it wouldn't be the end of the world if you had to get a new stronger power supply if/when you decided to sli 2 cards. For the time being 1 970 along with the i5 is plenty for 1080/1440p gaming.

Here is the spec sheet for that superflower psu.
http://www.super-flower.com.tw/products_detail.php?class=2&sn=8&ID=4&lang=

An oem license generally means windows can only be installed on one pc. If you change motherboards (which the os license is tied to) then there's a potential you might have to buy another copy of windows. If you used a retail copy of windows, then if you switched the motherboard you can reinstall as many times as you like provided it's only registered on one machine at a time. This was an issue with win7 however I don't believe it's an issue with windows 8. Oem copies are a bit cheaper, but the idea is that those licenses are intended for system builders to install on a machine to sell to a customer. They weren't really intended for people to purchase to install on their own machine, which is what retail copies are for.

Again this is a matter of licensing, legality and support. If you had an oem copy of windows and for some reason had to change the motherboard (say yours died), even switching for another z97 motherboard - you may have to call m.s. and see if they will allow you to reuse it and they would have to reissue you an authentic license to be legit. It would be up to their discretion.

This isn't to say what's physically possible, but going by the legal uses of windows according to microsoft. For a home built personal pc, windows 8 (not 8.1) home/pro can use an oem windows copy. For windows 7 home/pro or win8.1 home/pro a full retail copy of windows should be purchased.

http://www.microsoft.com/oem/en/licensing/sblicensing/Pages/windows-licensing-for-personal-use.aspx#fbid=rPiIHdfiKm8