You will be able to connect only two external because HDMI and DisplayPort use the same internal port so you cannot use both at the same time. 

And if you use VGA + HDMI or VGA + Display port the system LCD will be turned off. 

http://www.displayport.org/cables/driving-multiple-displays-from-a-single-displayport-output/

this is one  way you can go beyond 2 monitors, I run a M18X R2 and using its HDMI and VGA it does infact shutdown the laptop screen ..

also something like this: http://ca.startech.com/AV/Splitters/DisplayPort/Triple-Head-DisplayPort-Multi-Monitor-Adapter~SP123DP

 but requires display port  monitors