The rapid expansion of inverter-based resources poses growing challenges regarding harmonic resonances and grid stability. This paper presents and evaluates a measurement-based modelling and simulation workflow that enables impedance-based stability assessment at the plant level to identify critical resonance conditions. For this purpose, differential impedance spectroscopy was used to characterise inverters and plant components in a laboratory setting. These measurements yielded frequency-dependent Thévenin equivalents and enabled the parametrisation of generic library models. In combination with the documented plant topology and equipment data from operating PV parks, plant models were derived and validated against field measurements, showing good agreement in the fundamental characteristics of the simulated and measured plant impedances. Furthermore, resonance stability was assessed for various scenarios at selected points within the plant using the impedance-based stability criterion. The results demonstrate that measured unit impedances, combined with plant topology and component data, can be used to estimate plant impedances and assess resonance stability already during the planning phase. This approach can support the design and certification of PV plants by identifying potential critical interactions before commissioning.