Study of low-mass protostars provides a window into the early formation of Sun-like stars and planetary systems. An existing theoretical framework describes many aspects of the star formation process. However, in practice the time history is uncertain because key parameters such as protostar mass and disk accretion rate are poorly known. Here we present a method to determine the disk accretion rate using time variability, based on Spitzer Space Telescope light curve data. We go on to describe ways to measure protostar luminosity using SOFIA Airborne Observatory data. Then we discuss modeling of CARMA and ALMA millimeter interferometer data to determine protostar mass. The protostar L1527 is modeled in detail.