You can mix canned and dry together, and yes, you'd decrease the dry. I'm not sure why he's vomiting this often, but I'm almost inclined to say you might want to have some bloodwork done pretty soon. Or, who knows - perhaps his tummy will settle once you can get off of that awful Hills food. It's hard to say.
It also sounds like he may be sensitive to *something* else here too - with all of skin/paw licking issues. You may want to consider adding some digestive enzymes and and probiotic (sprinkle on food once per day) - as this can help support the small intestine as well as the tummy.
His picture is SO darling, btw!! Is Darcy named after "Mr. Fitzwilliam Darcy", btw
?