  We develop a comprehensive and flexible model for the connection between
satellite galaxies and dark matter subhalos in dark matter-only zoom-in
simulations of Milky Way (MW)--mass host halos. We systematically identify the
physical and numerical uncertainties in the galaxy--halo connection and
simulations underlying our method, including (i) the influence of host halo
properties; (ii) the relationship between satellite luminosities and subhalo
properties, including the effects of reionization; (iii) the relationship
between satellite and subhalo locations; (iv) the relationship between
satellite sizes and subhalo properties, including the effects of tidal
stripping; (v) satellite and subhalo disruption due to baryonic effects; and
(vi) artificial subhalo disruption and orphan satellites. To illustrate our
approach, we fit this model to the luminosity distribution of both classical MW
satellites and those discovered in the Sloan Digital Sky Survey by performing
realistic mock observations that depend on the luminosity, size, and distance
of our predicted satellites, and we infer the total satellite population that
will be probed by upcoming surveys. We argue that galaxy size and surface
brightness modeling will play a key role in interpreting current and future
observations, as the expected number of observable satellites depends
sensitively on their surface brightness distribution.
