Shrimp count is the number of shrimp in 1 pound. The larger and heavier the shrimp, the fewer it takes to weigh 1 pound, and therefore, the lower the count. If you try to substitute one count for another, your recipe, which was developed by weight and volume, may not be successful.
For the creamiest texture, use whole-milk ricotta.
Garnish the casserole with chopped parsley.