Although late to this thread,
I don't think you would see much of a performance difference between buying a 3570k and a 4670k. Undoubtedly the 4670k will be better, but not by much, and IMO the price difference is not worth it.
As for graphics cards, as far as fsx is concerned, Nvidia is the way to go, and the GTX 770 is a good choice. However, if you game in general, getting an AMD 7970 is a very good bang for your buck card, as it has great gaming deals and optimised for a lot of games. However, if money isn't a constraint, a gtx 780 or Titan are both great.
For motherboard, of course get the right socket, either lag 1155, or 1150. The advantages of a Lga 1150 mobo, is that it allows more USB 3.0(I think 6) slots on it, and 4 SATA 6Gb/s ports instead of only 2, so you could have 4 SSD.
I have also heard that Intel may block OC'ing on any mobo that is not Z87 in their series, so maybe the 4670k is the way forward? Also get a mobo that will allow two way or three way SLI for potential expansion. I have 2 GTX 670s.
For the PSU, get at least a 750W and certainly don't get the cheap once. Get a bronze certified and 80+ certified. WIth that, that allows OC'ing, SLI and plenty of fans etc. A good PSU allows a lot of expansion.
For HDD etc, I recommend having a 60gb SSD, a 500GB SSD, 1TB HDD and a backup 500GB HDD. I know it is 4(!) hard drives, but the 60GB SSD is for the OS, the 500GB SSD for gaming and FSX(seriously it is a joy to use having fast loading speeds), a 1TB HDD for general storage, like holding installers for fsx, and a backup 500GB HDD, in order to backup the 500GB SSD, as after 1-2 years, the SSD could potentially break, they aren't so reliable.
Casing, I have a Corsair 650D, but honestly, anything with plenty of fan expansion, allowing at least 240mm radiators, anything with good airflow is worth it.
Cooling for CPU, swiftech look very good, but I use a H100i, and that on a 3570k or 4670k could easily push the CPU beyond 5Ghz+ considering a 3770k at 4.7Ghz is 47 celsius!
Your PC is very money dependent, but I hope this is a general guide.
Peter