Ok. Long post incoming
SSD's will NOT affect graphics ingame. They will affect loadtimes, but not by too much, and their main use is heavy file transfers (ie a server or a heavily used workstation comp) and they will drastically increase boot time.
When I say HDD, I refer to both SSD's and traditional mechanicals drives - which is not technically correct. What I mean is, you will find that even a 120GB SSD will fill in no time if it is your only drive.
Until SSD prices drop enough to justify it, for normal users like us they are purely OS drives with maybe one game and commonly used applications.
In your case, definitely get a 500GB or 1TB mechanical, you will appreciate the space more than the speed, especially when they're so cheap atm.
In regards to your question about the Samsung, the F3 is better. You will definitely be wanting a 7.2k drive, and it is still the fastest on the market. Definitely get the F3.
In terms of SSD brand, get an Intel X-25. They are the best ones out right now, and along with the Samsung, cheap too

With your hard drive, expensive doesn't always mean better. It's similar with RAM and some cases (Lian Li's K series are quite cheap, but excellent cases).
Will you be overclocking? If yes, get an 890FX chipset, they overclock better. If no, get an 890GX chipset, they're cheaper. Go Asus or Gigabyte, and ensure you have an AM3 socket, DDR31600 support (at least), USB3/SATA3 (but not ONLY those, you will want some SATA2 and USB2 ports... they are backwards compatible, but you want to be safe), and one 16x PCIe lane with the capacity to do 8x/8x in dual GPU configuration.
For the CPU, I would personally go for the 955 quad, because hexacores don't show that much of a difference when gaming, however if you are set on the hexacore, get the 1090, it's the only one worth getting IMO.
Memory wise, you will probably not need any more than 4GB if you are gaming. Get either G.Skill or Corsair and make sure it is 1600MHz with CL8, CL7 preferred. I don't understand your thing about the 1TB external, Memory (RAM) is unrelated to HDD's. Never bother with the max amount of RAM a mobo will support. You will never need this much unless it is a workstation PC or a server, and more RAM/higher frequency RAM actually makes overclocking more difficult.
750W will be plenty, but ensure you get a good one. The best out right now would be the Seasonic X-750, but it is very expensive, and I'd just go with a nice Corsair or Enermax (or cheaper Seasonic), preferably modular because it makes cable management easy. The lovely thing about the X-series is the fact that it is so efficient. You can comfortably run a computer with recommended spec of about 820W on them (Note, when determining how much power your comp will need, go by the recommendation on the GPU and add 50W, it tends to work out nicely, and if it doesn't, you've got an awful PSU or their recommendation was wrong. GPU's tend to require slightly less than the recommended spec, so by adding 50 you give yourself enough room). If you want to run dual cards in the future, make sure you check the recommendation for two cards, and get a PSU with that amount.
In terms of graphics, get the EVGA 470 you linked. It is a reference card, so it should have voltage control enabled for a nice overclock if such things grab your attention.
Mouse and keyboard are really personal preference, but I highly recommend either a Logitech Mx518 or a Razer Death Adder V2, both mice are very good quality and have more sensitivity than you'll ever need
For keyboard, I recommend the MS Sidewinder X4 or Logitech G15, again, both wonderful keyboards, I've used both of them and prefer the SW x4, but the G15 is nice too.
For monitor, I have to say that the best ones are Samsung and Dell. At this point in time an LED monitor would be preferred, and a 24" is a nice size, with res of 1920x1080 and preferably a 2ms response time (although 5ms is plenty fast enough). Make sure it can do 75Hz at least, because a 60Hz monitor can look quite blurry, and it's unpleasant to use a lot of the time.
Afterthought: The Seagate Momentus is nice, and sort of worth the money, but I think you'd really be better off with a mechanical + an SSD, rather than both. You also mentioned you would install windows then put the mechanical in? I'd be careful doing that, as major changes can corrupt your install. Now I know this doesn't apply to RAM or GPU as I've done both of those, but I've never run more than one HDD so it might be a good idea to be safe and put both in. It shouldn't be too difficult to tell which is which.
Do not format your SSD on first install, and try to avoid it as much as possible. Mechanical is no problem, but formatting an SSD can reduce the life of the NAND's and stuff up TRIM support.
Laymans terms, it'll make it die quicker.
I really hope this helps you, because it took me 20mins to type out

Let me know if you have questions and I'll try to answer them. Sorry for the wall of text, too.