If this guy is wanting mainly to do 3D work then I'd also look to make the Front Z axis plate the narrowest and lightest you can make it.
Keep the Y axis bearing spacing wide but bring the Z rails in the most you can get away with and have light narrow front plate.

3D requires fast directional changes and high acceleration so anything to help here will speed up the job.!

Regards the motor access you have enough width and height in that plate to cut an access hole for motor and still not lose any strength, will cut weight too.! . . .Win win.!!