Building a new computer, need help filling in some hardware

GPU: Perfect!
PSU: The XFX has Golder 80Plus certification. Go for it. The other one only has Bronze.
CPU: Great!
Mobo: You buy a mobo based on what I/O ports you want, inside and out. If you'll want SLI sometime later on, check if the board has enough PCIe 3.0 x16 ports. Just seeing the "Z" in an Intel-socket motherboard means it's one of the best boards for the price, well performing, could even handle OC.
Also, some mobos are themed (with red and blue and all that), so if inside eye-candy is your thing, go for that and a case with a side-window.
RAM: 8GB is more than enough. You can upgrade it later on and save money for now. (Maybe an even BETTER GPU? *wink, wink*)
CPU heatsink: Do you mean closed-loop WC or building it from a kit (open loop)? I personally don't trust closed-loops, though they do their job and cool the CPU down. For the money, I'd rather go with an air heatsink (some of them don't even need the fan to run, so there's no noise, which is better). It also depends on whether you intend to OC.
Case: Just choose whichever you like. Go to the site you want to buy it off, set your budget for it, and see them through. It's a pain, choosing a case, so just scroll through and click the first three you like. Watch out for the size! Your PSU and mobo have to fit (though most Mid-tower cases will, anyways). For least noise, I recommend lots of fans (preferrably at low RPMs), LED fans are eye-candy, so it's up to you with those. A necessity are air-filters, at least on the front and over the PSU! Side-windows are a must, especially if you know how to arrange the cables neatly and will have LEDs and suck inside. (Showing off is always good, eh? )
Monitor: Up to you. Though the lower the resolution, the longer your GPU will be able to max out games!
Optical disk: Just choose one. 90% of the ones on Newegg are good for installing games and watching movies. But you'll have to invest more in a Blu-Ray one!
OS: Get Windows 8.1. AFAIK, there's only two versions, so go for the cheaper one (the costlier one doesn't add much unless you're a business man).

EDIT: About SSDs and HDDs:
If you can, get SSDs instead of HDDs.
Having two hard drives usually means that you have the system installed on one and the programs on the other (people argue about the best combo).
The truth being that more SSDs, the merrier. Buy as much storage as you *think* you'll need. Most cases have at least 5 SSD/HDD mount places, so upgrading storage isn't an issue.

Also, about system fans:
Get as much as your mobo can handle, install them and make them run at sub-950rpm. That way, they'll be pushing air all the time, but won't be noisy (and the inner components (heatsink, GPU) won't need their loud fans).
Once you're out of mobo fan ports, get some ultra-slow and ultra-silent fans and just stack them inside the case, as many as you can, and connect them via Molex (to the PSU). You'll always be able to turn those non-molex fans off!

Quite a lot to discuss here.

CPU+Motherboard
There is nothing wrong with going for that combo, especially if you are confident in Gigabyte. You are looking amongst high-mid boards, and the ASrock Z87 Extreme 4, Gigabyte Z87X-UD3H and Asus Z87 PLUS are all very similar in features and performance. The ASRock is usually the cheapest (so best value) but the combo deal probably wipes out that advantage.

Graphics
Nothing wrong with a GTX770, but they don't really offer the best bang for buck right now. I haven't seen any evidence of an incoming price drop, but given AMDs latest launches, I'd assume it can't be too far off until they get a bit of a reduction, as right now they cost a lot more than a 280X.

PSU
Both of those PSUs are very nice, but I'd probably advise against a 750W. For a single GTX770, a 600W PSU is plenty, but if you want to have the ability to SLI in the future (especially with a CPU overclock) then something above 800W is advisable.
Personally, I'd drop to a 600/650 unless you have a definite plan to double up on graphics somewhere down the line.

CPU Cooler
If you just want a quiet, cheap solution, you can't go wrong with the CoolerMaster Hyper 212 Evo, you'll see it recommended in almost every thread. If you want high end performance and quiet volumes, have a look at the Noctua NH-D14 or Phanteks ph-tc14pe.
In the hybrid air category, something like a Corsair H100i is both effective and not outrageously expensive, but it can get very noisey and requires a double fan slot for radiator.

RAM
If you just want value, find the cheapest 1600Mhz 1.5V kit you can. They start at around $65 for 8gb. You can spend more on fancier heatsinks and quicker speeds, but it's not a great return on investment. You don't need more than 8Gb for gaming, but if you multitask or run multiple instances of games, then more might be useful.

Case
These are totally subjective so suggesting anything specific is a bit pointless. Your budget is generous, so you might as well get something of decent quality. If you just want something straightforward and smart, the Corsair Obsidian range is quite nice, as is basically everything Fractal Design make.

OS
Hopefully someone with a more precise knowledge than me can help you here, but as I understand it, OEM version will give you a single install and registration to a specific motherboard. A retail version can be transferred. There are also differences in the level of support you are entitled to, and ability to upgrade versions.

Storage
If you can't fill 120GB then you can just have a single drive. Most people will comfortably rack up a few hundred GB in junk, and large capacity SSDs can get very expensive. The obvious solution is to use a small SSD as your Windows drive (along with any other select applications) and then use a standard HDD for anything else. As an example, I'm a cheapskate so only bought a 60Gb SSD. I have 6TB of additional conventional storage.

It's all your preferences, really.
First decide how much ram you'd like, then see Newegg on their offers. The one Rammy posted is great, but if you'd like better performance or different colors, it's all on you.
As for the monitor, there isn't much we can recommend. Find something with at least a DVI port (avoid VGA!) and 16:9 ratio and you're good to game.