For your budget, i think it might be a little difficult to fit in that 4gb GPU, since right now the prices are quite high. If you want to go into the FX world, you can't go wrong. Are they the best in the world, no. But They are still none the less a great chip. Right now you can get an FX-6300 for about $120, and FX 6350 for about $140 ...and fx 8320 for $160 and and fx 8350 for $180-200 Depending if there are deals going on with newegg (which is often). All of them i think would be great for what you would use it for, and they all should last for the next 2-5 years (i might be a little optimistic there). Right now the cheapest 290 is the MSI r9 290 which is going for like $460. All other GPU's are going to be 500 and up, so if you are going into the 1000$ range, this will take up half your budget. A good psu, like stated by others 750+ would suit your needs and those can range from 70-160 depending on quality and whether you want a modular or non modular design. I personally like the corsair line of PSU, but thats all on you. Mobo, if you don't plan on OC'n then you can go with a cheaper MOBO that has 4+1 phase power, which are cheaper. If you want to OC go with something that has 8+2 phase power, like a gigabyte 990fxa - ud3/5. Had mine for 3 years, no issues and great price (~130-140$). Ram if you want 8 gb, your looking at another 60-90, newegg always has good prices and sales going on with ram. G.skill sniper / ripjaws or Corsair vengence would be really good. If you have a HDD already then theres is money saved, if you want faster snappier responses, go SSD. Those are getting cheaper nowadays too. You can either do what most like to do which is get a 60gb SSD and use it for OS only (it makes a difference trust me) and then use an HDD for other files/games/media. OR just go straight SSD's, but that will cut into your budget. Case? If you already have one great, if you want a mid tower, they arent that expensive, if you want a full tower, then those are pricer (100-200 on average). CPU cooler, if you don't plan on OC'n, you'll be fine with stock cooler if you dont mind the noise, it'll spin up to 3000 rpm or higher and will be kinda loud. Another option, Hyper 212 plus or hyper212 evo, both less than 30 bucks (sometimes less than 20) and compete with many high end coolers. I think that is the gist of it all. to recap:
CPU: ~120-180
GPU: ~460 - 500+ (you could also do an r9 280 3gb)
PSU: ~70-160
MOBO: ~80-150
RAM: ~60-90
SSD: ~60-170 (60gb/120gb/ and some 240gb ssds are included in this range)
HDD: ~80-100 for 1 tb
CPU: ~20-30
... I realize my prices are not exact, they are approximation just so you can get an idea of what to look for and how much you might be spending. For 700 for sure you will have a really good gaming rig. shop around and look for deals, newegg always has great deals / promos/ rebates. Amazon sometimes has good stuff too and every once in a while i find some good stuff from tigerdirect.
PS. I personally would not recommend going crossfire/sli, i feel there are just way to many annoying issues to worry about, and most new "next gen" games that have been coming out dont support crossfire/sli right of the bat, and the drivers that seem to be coming out seem to get worse. I know not everyone has these issues, but when i get into the forums i know im not alone. Just something to consider before you spend over a grand on GPU's alone. One strong card is all you need IMO. Hope this helps.