Through new NOEMA (Northern Extended Millimetre Array) observations of the M51 galaxy, our team is trying to address the gap between galactic and extragalactic CO and CO isotopologue studies. As part of the SWAN (Surveying the Whirlpool at Arcseconds with NOEMA) survey, this data maps 13CO, C18O and multiple dense gas emission lines in the inner 5 x 7 kpc2 at the unprecedented resolution (~125 pc) for a galaxy of this type. We analyze how the spatial distribution of 13CO(1-0) and C18O(1-0) emission in M51 varies with opacity and molecular abundance, revealing underlying gas conditions across diverse environments (nuclear bar, molecular ring, spiral arms and interarm regions). We find a moderate positive correlation between the 13CO(1-0)/C18O(1-0) ratio and galactocentric radius and a moderate negative correlation with star formation rate surface density. While the overall trends align with previous kiloparsec-scale studies - suggesting that the physical and chemical processes governing these emission lines operate similarly across both scales - variations across environments suggest localized processes play a larger role than previously expected. To further pin-down the impact of stellar populations and feedback processes on the interstellar medium, we attempt to capture the star-formation process in its entirety by combining SWAN with JWST-FEAST. Together, these datasets offer a novel view into the physical and chemical conditions closely linked to recent star formation.