You will probably have an issue with the 183.5 dimension on a 4 X 8....
Some CAD software will read .txt files (from XL) known as CDF files (comma dilineated files). the data is normally ordered in X,Y,Z format. I doubt that it will genereate closed profiles as you described
You have the conversion process correct, and even if you cannot read from XL,the nesting program will read multiple .dxf files.
The CNC router is still the way to go,