Expensive yes, but bear with me...
http://pcpartpicker.com/product/c298TW/asus-monitor-mg279q
You can get a 144Hz, Freesync, IPS monitor for $500.
If you want to play CSGO, it's absolutely incredible. You get incredibly SMOOTH gaming. Conversely, if you have a 60Hz monitor you either have to put on VSYNC which makes it pretty SLUGGISH for shooters, or you have to turn VSYNC OFF which gives a lot of screen tearing because you're getting partial frames mixed together every time it updates (60X per second).
Yes, it's expensive though you can get two, cheaper monitors for non-gaming purposes.
You may also want to get an RX-480 graphics card for $200+ when it comes up then add the other monitors later. The RX-480 and this Freesync monitor would be a truly awesome experience.
(just FYI, but Freesync ideally needs 2.5X the max to min ratio for asynch mode to work properly. If it's 30 to 75Hz it's okay, but if it's 30Hz to 60Hz it's not. This one is either 30 or 40Hz all the way up to 144Hz though. A lot of Freesync monitors suck because of this. Heck one recent model is 45Hz to 75Hz meaning you either have VSYNC ON or VSYNC OFF when above or below this so games are toggling in and out of the smooth mode a lot which is a HORRIBLE experience.)
Other two monitors:
Some people get smaller monitors and turn them 90deg which is pretty useful for many programs. If so, then calculate so it matches the vertical height of the screen not counting the bezel.
Either way, I'd get two, identical monitors. There are plenty of choices around $100 that are pretty good. Might want:
a) IPS (if main screen is IPS)
b) 1920x1080
c) INPUTS should match what graphics card or cards can output.
Summary:
You may not care at all, but if it was my money then I'd get the $500, 2560x1440, 27", Freesync monitor, buy the RX-480 when available, then get the other monitors as budget allows.
*again, FREESYNC can be pretty awesome, especially for shooters. I don't mention GSYNC because it's out of your budget, and also the new RX-480 is the best value card you can get IMO if roughly $200 (MSRP, and 4GB version not 8GB) is your max budget.