Looks to be a good setup. Though, you wanting it to hold out for 3-4 years can depend on many things. The i5s tend to hold good for the many years or more especially if you get a good overclocking on the chip. I actually ran a i5 Sandybridge at 4.8GHz for over four to five years no problem *Note: It was fully water cooled though*. At most you may have to upgrade the GPU or buy a 2nd one of the same card, but then you get driver issues and issues with games supporting SLI/Crossfire when going two cards. For GPUs, depends what you want out for it, bang for buck or most power you can go plus how well the drivers are developed. Personally, AMD cards are nice cards plus great folders too. The Con: make a lot of heat and noisy, and eat electricity. The Nivida cards are expensive, but do deliver great power, less noisy, drivers tend to be developed better, and not as much a electricity hog *Unless, you do some crazy overclocking*. Plus, the EVGA Nivida cards have one of the most unbeatable warranties out there for GPUs. If you buy a used one off a person, if it still under its warrenty EVGA will still replace a bad one even if you not the orginial buyer.
On Western Digital Blacks, another difference is the warrenty. Blacks have a longer warranty than the Blues. Instead of the two years on Blues you get five years on Blacks. I really never noticed them being noisy than again I have like over 8+ fans at any given time running in my rig, plus the folding rig making its racket with its jet engine sounding fans to keep that 7970 cooled off.
On the RAM, whats the MHz and timings? I know Vegeance are great RAM, still got my 16GB set. Just curious what speeds the set you looking at are running at.
Also, one tip, pick a case first before anything else. Computer case is the foundation and will affect which mobos, cooling setup, the amount of HDDs/SSDs, amount of fans/cooling setup, and video cards that can fit. Plus, it usually the computer part that you keep for many, many years.
I will upvote on the SeaSonics. Best dang PSUs you can get, unless you know someone who has one of the older model Corsair PSUs. Those things are made like tanks too. Got a six year old TX750 that still running to this day. But overall, I have only heard good things about the SeaSonics.
On CPU cooling, depending on what case you get can affect what you can install. Aftermarket air coolers are best bang for buck, but then you get the noisy plus their HUGE! All in one water cooling units are very nice, a little more cost, but then you don't deal with noisy of a air cooler. Only thing, making sure you got space for radiator to mount in the case. Full blown water cooling, depending if you get a kit or buy all parts sperate can vary by cost. Some of the kits can run for around 250-300 or full blown custom water cooling can easily get into the thousands on cost. The pay off is you get the best cooling and its custom, so if something needs to be changed. You can just switch a part out. Only thing, is be careful with water cooling, even the all in ones can get leak if faulty. Best pratice if going that route is laying papertowels or small cloths underneath or wrapped around connectors for the first run of a loop then allowing it to run for a few hours without the computer parts energized.