Characterising M dwarfs is the key to unlocking the properties of the most common planetary systems in our Galaxy. We present a multi-disciplinary analysis of the local M dwarf population, leveraging Gaia DR3, 2MASS, and TESS/Kepler datasets to provide a homogeneous census of stellar parameters. Our work specifically addresses the discrepancy between Gaia FLAME and empirical stellar radii, a critical step for the target selection of the ESA PLATO mission. We explore advanced techniques for abundance computation, including pseudo-equivalent widths and neural network-driven spectral analysis. To account for stellar noise in exoplanet detections, we analyse rotational periods and spot properties (size, temperature) using EXORAP multiband photometry and high-resolution FUV/X-ray spectra from Hubble and XMM-Newton. Finally, we highlight our search for long-period planets and the use of CRIRES+ spectral synthesis to derive Fe, Mg, and Si abundances, providing chemical constraints for modelling the interior composition of rocky exoplanets.