Richard, Fine Woodworking did a shaker writing desk and it answers some of your questions. Not sure if you can see without a subscription, but it was a desk built by Christian Becksvoort. He puts a drawer in a relatively shallow apron. The key was the drawer front was the full width of the apron. There was a drawer support frame attached to the front apron stubs at each leg that spanned the front of the desk.

His desk was 30” high with a 3-4” wide apron.