When designing shapes, with holes what is the smallest size that I will will I be able to produce with your chemical Etching (Milling ) machines?

Any shapes whether complex or simple can easily be generated.  The only real limitation is the size of the smallest hole is generally 0.1mm when working with material that is thinner than 0.1mm.  When working with materials that are thicker than 0.1mm holes can generally be produced with a minimum size equal to or greater than the thickness of the material.