A single large SSD, 256GB+ is fine for Windows and FSX both. From my testing of various HD configs, that is better than Windows on a spinner and FSX on an SSD, or vice-versa.
Ideally you'll have 3 drives. A small(64-128GB) SSD for Windows, a larger one(180GB+) for FSX and a 1TB+ mechanical for other apps, storage, and backup.
Depending on the motherboard, you will usually have at least 2 SATA III(6GB/s) and 4 SATA II(3GB/s) ports. Be sure the Windows and FSX drives are connected to SATA III(6GB/s).
As others have noted, the Samsung 840 offerings are great. The 512GB Pro in my rig is the only SSD that has ever crossed my bench that meets/exceeds it's advertised R/W speed.
Use your selected motherboard's QVL(Qualified Vendor List) to help select your memory. The stuff on that list is known to work, but, are not the only sets that will. Some listings may be older and no longer available.
Grab the fastest, Lowest Latency, 8GB set you can afford...Don