A comprehensive experimental study of the initial stages of electrochemical dealloying of the model system Cu3Au (111) is reported. Using a unique combination of advanced surface-analytical tools, we illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential. We then further use the observed structural transitions as a reference process to evaluate the mechanistic changes induced, first, by halide additives to the electrolyte and, second, by a thiol-modified surface. Halides lead to faster surface kinetics and accelerate the formation of porosity, whereby iodide additives induced a different surface morphology involving precipitated copper iodide layers. Thiols are studied as a model inhibition layer, as they block surface diffusion. One result is that the initial ultrathin Au layer is stabilized, and the intermediate island morphology completely suppressed. For the critical breakdown or pitting potential, an anodic shift of about 100mV is revealed. Thiol modification results accordingly in peculiar surface microstructures in the form of micro-cracks exhibiting a nanoporous core. This opens up new possibilities for producing micro-structured porosity. Understanding initial dealloying is therefore shown to enable the developing surface and porous-film morphology to be controlled and directed.