Looking for opinions on this build, and how long do you think this gaming pc will last before needing upgraded?

The gpu was covered, but I would save up for a GTX 770 if you can, it should be able to play just about everything at max at 1080p for now with a few exceptions such as games that are poorly optimized and even cover you into the near future. If High is ok then the GTX 760 isn't a bad gpu. Specially if your be happy with the 30fps as a lot of the newer games will probably net you 30+ fps on "high" @ 1080p. I got a GTX 770 and I'm glad I went the higher end.

I would also save up for a better quality Mobo, as lower end Motherboards are liable for failure and sometime they will take out everything hooked into them when they do fail. (I had this happen so know first hand. I usually go Mid range at minimum.

Ram was covered but another reason for 2 sticks is if that 1 stick goes bad you have NO ram at all, at least if a stick of ram goes bad your have SOME ram rather than none while you replace the bad stick through RMA process or what have you. Plus you do get the benefit of dual channel which as firo40 said is faster.

The psu is ok, I have the 600W version powering my AMD build (Non-OC AMD FX-6300, AMD R9 270 Factory OC'ed to the R9 270x's specs.) and it works great! Though I will be replacing it with something better. I trusted it more than other psu's. My current build has an OCZ Fatal1ty 750W 80+ Bronze powering it. The psu seems more of a personal experience as I've bought the Corsair CX Semi-Modular series before and never had a problem with it. Ever. But if I could I would go with Seasonic, or XFX as those are really good psu's.

The psu is the heart of your computer, without a proper one your stuff won't get the required power and could be fried. If the psu is overloaded it could cause a surge which would then fry anything connected to it upto everything, or you could luck out and it doesn't and you just replace the psu with a better quality. I, again am a example of that, I've lost a cpu (AMD Phenom II x4 965 BE, AMD Radeon HD 5770 gpu, and a full computer to various bad psu's, once I wised up I vowed never to underestimate the psu again.