Yes, since we are talking about your workbench : ) and not drifting off on topics that should be under their own headings so that in the future people can search and find them easier ( hint, hint) : )
My initial question about top thickness was to lead into suggesting an additional thicker/ studier top. Might even be a good idea to set it up with studs located for your lathe feet and motor mounts pre installed so you don't have to pull out the drawers to access the back sides anytime you need to make adjustments. Then do some top down attachment bolts threaded into the frame of the cabinet. That would also allow any future changes to be made without unloading/ removing drawers.
Nice Idea on the sewing machine motor! do they have the necessary torque? Also is that speed controller included with the motor and what size pulley is on it?
Thanks Ken H in AZ
Ken H