subd all the way,
start with “strips” that make up the flat front surfaces, and make your way back in space using extrude edges.
bridge to get the supports between the layers,
then bridge again between inner and outer surfaces to get the holes.
Save the holes for last, you may need to subdivde the model several times to get enough faces to create them,
or convert to nurbs and make them with traditional tools, (project curve, trim, blend srf)