You can add up to 1 pound of shrimp to this recipe without altering the amounts of the rest of the ingredients with similar results if you want more shrimp but the same amount of sauce.
I use a wheel of Boursin to season the grits as well as 1/3 cup of grated Parmesan-Reggiano ... I estimate that you need at least ½ pound of jumbo shrimp per person.