We present the results of spectroscopic follow-up for 1897 low-metallicity star candidates, selected from the Best and Brightest (B&B) Survey, carried out with the GMOS-N/S (Gemini North/South telescopes) and Goodman (SOAR Telescope) spectrographs. From these low-resolution (R~2000) spectra, we estimate stellar atmospheric parameters, as well as carbon and magnesium abundance ratios. We confirm that 56% of our program stars are metal-poor ([Fe/H]{<-}1.0), 30% are very metal-poor (VMP; [Fe/H]{<-}2.0), and 2% are extremely metal-poor (EMP; [Fe/H]{~7.25) and 97 to Group II (A(C)<~7.25) in the Yoon-Beers A(C)-[Fe/H] diagram. Moreover, we combine these data with Gaia EDR3 astrometric information to delineate new target-selection criteria, which have been applied to the Goodman/SOAR candidates, to more than double the efficiency for identification of bona fide VMP and EMP stars in comparison to random draws from the B&B catalog. We demonstrate that this target-selection approach can achieve success rates of 96%, 76%, 28%, and 4% for [Fe/H]<=-1.5, <=-2.0, <=-2.5 and <=-3.0, respectively. Finally, we investigate the presence of dynamically interesting stars in our sample. We find that several VMP/EMP ([Fe/H]<=-2.5) stars can be associated with either the disk system or halo substructures like Gaia-Sausage/Enceladus and Sequoia.

Cone search capability for table J/ApJ/913/11/lmcand (Low-mass star candidates observing details (Table 1), photometry (Table 2), stellar parameters (Table 3) and phase-space information from Gaia EDR3 (Table 4))