Seriously, if you're gonna try to get into FMX, consider a 250 2-stroke. The 2-stroke is preferred by the majority of the dudes who hit the ramps. Less bogging issues, lighter, easier to throw around in the air, different center of gravity, no decompression braking, more grab points like around the seat/exhaust area, good power/acceleration, etc.... It's also a good all around bike for MX and hitting the trails too. And less maintenance that a 4-stroke.
As for 250F's, if you go with the 2003, be ready to drop $2-3k into the motor, as you're bound to have problems sometime in the near future.