You may find one or more local shops/stores that can assemble the parts for you(for a modest fee, of course). If you want them to overclock the components as well, that might cost substantially more(where it may take 30 minutes to assemble the system and a bit longer to install the os and get it up and running, the initial tests for finding a potential overclock as well as overnight torture testing for long term stability might cost even more if they offer it despite the fact it's less labor intensive and more waiting around and using their electricity to perform tests). If you haven't already, you might try searching youtube for videos on how to put together a system.
You may end up doing some research yourself to find best practices in overclocking these components. Again, while building a system yourself for the first time can be a little scary, you would feel a real sense of accomplishment if you managed to do it yourself and it boots up your first try turning on the power. If you are careful in selecting a build location(maybe a cleared off kitchen table or dining room table if the floor is hard and flat) and start yourself grounded with occasional breaks to ground yourself again(staying off carpet and maybe even being barefoot help a lot). Pay special attention to mounting the mobo into the case. read all those directions that come with the case and all those directions that come with the mobo.
You might consider whether you have any friends in the hood that are big enough computer geeks that you could ask them to help you put the system together(maybe offer them a few bucks). They might even enjoy helping you overclock the cpu and video card(again, for a few extra bucks). That way you can get to know a friend better in regards to one of their interests you previously maybe weren't so into, learn a few things for a time down the road when you may want to get a whole new system again, and just feel more connected to the hardware by being there and even getting your hands dirty in the process(not really dirty, more a figure of speech). As far as tools and what not, you don't really need an anti static wrist wrap to protect circuitry from static shock(just ground yourself to start and every so often during the build). It's a good idea to have a phillips head screw driver with a magnetic tip( just enough magnetism to pick up a dropped screw, not near enough to damage any components). Maybe a flashlight.
I almost forgot. I think I read about some stores that offer to send out a tech who walks you through building your own system. You might consider that too(but I think it might be a bit expensive). Your first build will probably take closer to an hour to put together. It's only after you've built a number of systems that time drops to under a half hour. The inital stages of overclocking a part may take a few hours plus one (or more) overnight stability test(s) during which you will most likely be asleep. If you want more details about handling components or grounding yourself, let us know. Same goes for general advice on how to overclock a cpu or video card.
You may just want to build the system(or have it built/ a combo of the 2) and load the OS/apps/games and see how you like the stock performance first. If it meets your needs, you may not need to overclock(although will probably want to a least overclock the cpu for guild wars 2). You could overclock the video card later if need be to get more life out of it(or if you find overclocking fun you may want to go ahead and do it for the video card too). Prime95 is a good way to stress a cpu far more than any game will(free download) and Furmark is a good program to stress a video card more than any game will( another free download I believe). Turn you cpu and gpu fans up as high as your ears can tolerate, and start testing the cpu first looking for errors(or rather error free test runs ideally) with intervals of say 20 minutes testing followed by 20 minutes of idle time. Maybe change the clocks straight away from 3.4(stock) to 3.7 (that's 980BE speed). If no errors and temps are ok, go ahead and try 4ghz. if you get errors(I imagine temps would still be ok), try bumping the voltage up a bit and test again. If you are error free and temps are alright, then consider an overnight test. If you get no errors and monitoring software shows temps stayed decent(free monitoring software can be found online too or may even ship with the mobo as it does with many) that is a safe overclock. Don't exceed 110% or stock voltage or +.1 volts, which ever comes first.
Cpu overclocking may go fairly quickly, actually if you don't mess with the base clock and just use multipliers. Overclocking the video card is similar, but with more variables(gpu mainly and ram as well). You can adjust fan speed and max tdp in the driver software. You can use a program like msi afterburner(free) for adjusting clocks and monitoring temps(you may do these things in the mobo bios for the cpu or by using software that comes with the mobo). Start with a 25mhz increase on the core and go from there(you may get from 860 stock to as much as 1200 some mhz). After overclocking the gpu, start the process over with ram. This is different since both amd and nvidia use error correcting ram in their cards since the hd5000 series and the gtx400 series respectively. That means when ram frequency is too high, instead of errors you will see a slow down in performance(operations start taking longer as the ram takes time to fix the errors). forgot to mention when you reach limits of voltage or temps(70s for gpu, not sure about cpu), back off a bit and test again(25mhz bumps for gpu and vram). you will use more power when overclocking(linear increase for clock speed bumps, exponential increase for voltage bumps, combination for both) but that xfx 550w is more than up to the task(you could even throw in the likes of an overclocked hd7970 later on with that overclocked 965BE if you wanted with room to spare). OK. Done for now. Hope this helps.