Are you going to be running any add-on scenery and or planes? Just to let you know, I have Orbx Blue Pacific Northwest, REX, GEX, ASE (5 cloud layers) along with PMDG's MD-11 with highish settings enabled and it starts to bring my PC down to mid 20fps when above Vancouver BC. When I'm outside Orbx's coverage, I have zero problems with performance. There are a ton of tweaks you can do for FSX to help improve performance.
For the i3, it will work but don't expect great performance on high. Google best CPU for FSX and read about other people's experiences. One of the better ones is the i5-2500K. I just don't know how the i3 will handle on very high settings. FSX is a CPU hungry game, don't forget that
Don't get dual card GPUs: Its not supported.