ok for easy use and so you don’t get confused in the engine i say align the mesh so that the front is pointing along the X axis
yes 0,0,0 is the exact center of the grid, use the co-ordinate system to set it, even if your just a little off it will cause problems in the physics editor
uvw mapping well thats up to you
well if the wheels are supposed to be like that then fine
then main thing is the placement/alignment of the root bone and then the alignment of the wheel bones otherwise you just get issues