The realization of the Future Circular Collider (FCC) at CERN requires a regional geoid model of unprecedented precision. Achieving such a precision requires a systematic analysis of all potential error sources, including measurement distribution, digital elevation model, density assumptions, and modeling parameters. This study presents the development and first results of a Geoid Closed-Loop Simulator tailored for the FCC region and implemented within the GROOPS software. The simulator enables controlled experiments by generating a “true geoid” through forward modeling and an “estimated geoid” derived with the Remove-Compute-Restore approach based on simulated gravity data. The influence of observation spacing and density assumptions on the “estimated geoid” are analyzed in this study. Results show that observation spacings finer than 1 km result in millimeter-level agreement with the reference geoid, whereas coarser spacings significantly degrade the solution. Incorrect density assumptions introduce systematic offsets of up to several decimeters, highlighting the model’s sensitivity to density errors. The developed simulator provides a robust framework for quantifying the propagation of input uncertainties into the final geoid solution and will support the future design and optimization of gravity measurement campaigns. This is an ongoing effort, and future refinements are planned.