For wildlife, I think a DX format body would be preferable. As to which lens, it depends on what kind of wildlife -- birds in flight would require a different lens than large mammals. Also, birds-in-flight would benefit from specialized setup, inlcuding a 600mm lens plus teleconverter, sturdy tripod, a gimbal head, flash extender, etc... The price for admission into this club is not cheap. Can it be done with less than the most expensive gear? Sure, but this type of photography requires reach, and unless you are willing to setle for mirror lenses, 500mm and longer don't come cheap.
For landscapes, either FX or DX woul be good; however, a DX body would hide light fall off or lack of sharpness in the far edges or corners.