Hey darkpivot -
Looks like a really good start you have. You might want to try going into Blender and modeling your cart in the same file as the reference spline you are using and then add a single bone weighted to the whole cart animate the bone along the reference spline then import the cart as a skeletal mesh and the animation will automatically come over with the cart model. If you are wanting this to be in first person you could also animate a camera along the spline, again in Blender, and then import the camera movement directly into Matinee (here is a link for that process: https://answers.unrealengine.com/questions/9061/request-fbx-camera-import.html). One caveat, I have only tried this in 3dsMax and Maya, but there should be no reason for this not to work in Blender as well.
Let us see what you get when everything’s together and as always if you are still having problems let us know,
Eric Ketchum