Hello Fred! Smoothing the basswood surface with a finishing plane is a fantastic way to get a smooth, flat surface.
You won’t hear me mention this method because most chip carvers cannot use a plane or scraper effectively to get the results you do.
Removing leftover pattern lines in the same way would be quite challenging especially if quite a lot of the surface has been carved.
From your post you know that we don’t want to flatten the tops of the sharp ridges. I recommend using a Tombow Sand Eraser to remove any leftover pattern lines.
They do the trick and break down as they remove the lines so they don’t affect the carving.