Here in Europe, Super-Flower SF500P14FG 80plus Platinum fanless is probably the same PSU as Kingwin STR-500. It seems to be a good option. How is it better than Seasonic?
It is exactly the same PSU. At any rate, with reference to the Seasonic, the SuperFlower/Kingwin is more efficient, it has better electrical performances, and it is less prone to buzz and whining: you may check the relevant SPCR review and also the JonnyGuru's one.
Please, take note: the X-Series IS an excellent performer. The SuperFlower is actually just slightly better.
Is Corsair as reliable as Crucial?
Broadly speaking, absolutely NO: the Crucial M4 128GB is more probably that not (along with the Intel 510 120Gb) the most reliable modern drive on the market (there is also the Intel 320-series which are usually way overpriced and however slower).
The M4 is also considerably slower at writing (expecially with large files) than the SandForce 28xx drives (like the Corsairs 3 & GT, or Intel 330/520, or the 3rd gen OCZ Solid/Agility/Vertex).
If the maximum achievable reliability is the top priority, more probably that not Kuzzia's advice is to be preferred.
What are the last generation Hitachis you mentioned? Is the Hitachi Deskstar I mentioned one of them?
I was thinking mainly to Hitachi HDS721010DLE630 (Deskstar 7K1000.D). There's also the bigger 7K3000 but which need a suspension, like the NoiseMagic NoVibes. I don't know the newest Deskstar 7K4000.
Noise-wise, alternatively you may think to the Seagate Barracudas (series DM001/DM003) which are to be favourably considered (it's faster than ther Caviar Black on large files, slower on small files, and it comes in bigger sizes than the 7K1000.D).
About the 7K3000 and Barracuda, you may check the relevant SPCR reviews.
Scythe Mugen 3 seems to be quite challenging to install. I've heard that the computer shop that could build up system might not like to ship the system with the Mugen 3 installed into it. I might consider Noctua also because of that.
I don't know if it's true (I'm referring to the Mugen3), but I'm used to build systems, and no mounting can scare me.
AFAIK, the only option to ship a system with a CPU heatsink mounted is the Gelid Tranquillo (source: Puget Systems), safety-wise.
Eventually, I wouldn't be worried about mounting the heatsink by myself, but I can't help about this.