I understand Steve. What you have done is fine and yes the steering wheel is a grab rail too.
As to the close holes on the mounting. That is perfectly aceseptable and is a standard machining practice to be the fastner diameter away from the edge.
On my boat the console is built with 3/8in Divenacell, but the area that the helm and control's are bolted to is 3/4in marine ply, for the reason's you listed above.
This is a pix where I modified the helm area after a change in the type control's was made.
This are is 3/4in marine ply.
