In this paper we perform a Fisher matrix analysis for future spectroscopic surveys (MegaMapper, MUST…) on the BAO, RSD, the non-Gaussianity amplitude, and the total neutrino mass. These surveys will have a large number of fibres (~20,000), and study the high redshift universe (z>2). In addition, we model the observations of a spectroscopic survey with free observational parameters (redshift range, sky coverage, efficiency threshold…), and we derive the optimal ones for non-Gaussianity and neutrino mass measurements, and study the fibre increase effect.