Scalable integrated process pathways remain a key challenge for ultrathin 2D device materials particularly for potential opto-electronic device applications. We employ operando optical and electron microscopy/ spectroscopy (Imaging ellipsometry, SEM, XPS) to systematically study reaction kinetics that underpin metal organic chemical vapour deposition (MOCVD) and scaled device integration of metal sulfide and selenide films. We focus on oxidation kinetics relating to material stability and dielectric interfacing, and exploring the role of salts to promote crystal layer formation. We adapt a Kramers-Kronig constrained variational fitting algorithm for spectroscopic imaging ellipsometry to demonstrate non-destructive, efficient, scalable mapping of multi-layer semiconductor heterostructures with 1 μm lateral resolution as well as operando capability. Combined with operando microscopy, this allows us to  systematically interrogate native oxide growth eg for HfS2 and HfSe2 as well as reveal the various reactions of excess chalcogen reaction products. High-throughput operando SEM allows to reveal various hot salt substrate corrosion phenomena, and how growth mechanisms are mediated by liquid salts.