I have a Dell Precision M6800, Quadro K3100M 4gb, RAM 16gb, i7, 17 inch FHD display. Apparently I can connect 2 external monitors via DP and HDMI ports. I have 2 Samsung P2250 22" FHD that I plan to connect.

How would you use such a setup? What would you display on the laptop built-in display and what would you display on 2 external monitors?

I was initially hoping to connect 3 ext. displays and create a 210 Degree view like here. Now I'm thinking to place laptop on the side for displaying flight software and maps and use external keyboard. That way I could use 2 external monitors for FSX but still not sure whether to display one wideview or place them in a V-shape (looking from the top) and display multiple views.

It is an individual preference in the end of the day, but keep in mind that if you fly with a display stretched across multiple monitors, it will put more load on the CPU and graphic driver than if you keep a view in one monitor and use the other monitors for undocked panel windows, third-party software, web pages, and any other external aids.  Such attempts is even tougher on laptops than on desktop computers.

I personally have three PC monitors, but they are all of different sizes.  I use the largest and widest display as my primary view, and use TrackIR to enhance my immersion as I use the other two monitors on either side for GPS, panel windows, and a lot of third party applications.