Need clarification when importing a First Person Arms skeletal mesh fbx

I am attempting to import into ue4.5 a first person arms skeletal mesh.
I believe I am missing some steps.

I am using the animation and rigging tools plugin in Maya to create and weight my skeletal mesh. I have followed the steps from the ue4 tutorial on how to export out a skeletal mesh fbx.

I built a full biped skeleton and brought in my arms mesh and weighted it. I then went through the finishing steps and built a rig through the tools plugin.

I exported out two different skeletal meshes to find out which one is going to best preform as first person arms.

The first export was the full biped, it worked but I got a warning that bones like the legs and the spine were not in bind pose even though I had it in bind pose/T-pose.
The second export was just the root, spine3, clavicles,arms and fingers along with the mesh.

Even though the second fbx export seems correct was this a good way to create and import a first person skeletal mesh? Any help is welcome.

I have been testing the versions of the first person arms that I have created. Refer to the question I posted above.
I have gone into maya and opened up the fbx file that has the full biped skeleton. I deleted the head,neck bones as well as the legs, feet.
I then exported out the fbx file with just the spine bones and the root. The arms mesh and the skeleton that it is weighted to were left as is.

Remember that the completed rig that I create animations with is still a full biped rig.

When I import in an animation fbx file I assign it to the skeletal mesh/skeleton that is now without the legs and head. My message log tells me that the animation fbx still has the leg and head bones. The skeleton asset does not have those bones.
My test animation works but I would really like to hear from the Unreal 4 guys at Epic. Is this a sound approach?