I really think you need to simplify. If for no other reason than imagining a line of ten people out your door ordering the same thing - what's the most efficient, cost effective and tasty beverage you can serve? You need to rely on your good old espresso machine and steam wand - you mentioned you're serving espresso, I'm assuming you have a manual machine? Or at least one with a reliable steam wand? I think that using shaved chocolate will be your downfall, if for no other reason, it just won't incorporate well, especially if combined with cocoa powder. Keep it simple!!