Whittaker models and the integral Bernstein center for GL_n

We establish integral analogues of results of Bushnell and Henniart for spaces of Whittaker functions arising from the groups GL_n(F) for F a p-adic field. We apply the resulting theory to the existence of representations arising from the conjectural "local Langlands correspondence in families" of Emerton-Helm, and reduce the question of the existence of such representations to a natural conjecture relating the integral Bernstein center of GL_n(F) to the deformation theory of Galois representations.