There is a way to generate a 3D sketch bounding box around a part. This would provide an X, Y and Z dimension for the part. Check the help menu for "Bounding Boxes". I assume this would be useful based on the description of stepping through the section view and measuring each slice since the box will expand or contract to the part. You also mentioned the max cross sectional area, so it may be a different value you are looking for that a bounding box would not help with.