With the continued success of Gaia, and the launch of TESS, we are entering a new era of precision stellar astrophysics and exoplanetology. I will begin by reviewing the main results of the KELT survey, and describe how it is a natural precursor to TESS, both in the sense that it complements TESS, and that many of the lessons learned from KELT can be applied to TESS. I will then show how, by combining the results from TESS and Gaia, as well as some planned or proposed surveys and missions such as the Milky Way Mapper and SPHEREx, we will be able to nearly directly and empirically measure, to percent-level precision, the masses and radii of stars with transiting low-mass stars and planets, spanning a broad range of the Hertzsprung-Russell diagram. Many, if not most, of these stars will also have six phase-space coordinates, detailed abundances (including abundances of many individual elements), and rotation periods. A subset will also have either directly-measured or model-inferred ages. In addition, we will also be able to empirically measure the masses and radii of their transiting companions and planets to precent-level precision. I will describe a subset of the transformative studies that this dataset will enable, including detailed tests of stellar isochrones, elucidating the 'radius inflation' problems of low-mass stars and hot Jupiters, and tests of whether terrestrial planets have similar compositions as the Earth, and whether these compositions correlate with the compositions of the host star. Finally, I will discuss the challenges associated with reaching these lofty goals, including following up of single transit events with TESS, and the likely limiting resource: precision radial velocity follow-up.