This contribution presents an integrated experimental–computational framework for the multiscale characterization and modeling of auxetic sheet metals with rotating-units microstructures. Perforated AlMg3 sheets exhibiting a negative Poisson’s ratio are investigated to enable reliable prediction of geometry-driven, anisotropic mechanical behavior in lightweight structural applications. The experimental program comprises uniaxial and biaxial tensile tests supported by Digital Image Correlation (DIC), providing high-resolution full-field strain measurements. Parametric studies quantify the influence of pattern size, perforation aspect ratio, and pattern orientation angle on global auxetic response, stiffness, and strength, providing a comprehensive experimental basis for model calibration and validation. On the numerical side, fully resolved microscale finite element simulations and homogenization techniques are employed to extract effective mechanical properties from the underlying microstructure. A representative volume element (RVE) is identified to link microscale deformation mechanisms to macroscopic behavior under varying loading conditions. Based on the homogenized response, a macroscopic anisotropic elasto-plastic constitutive model is developed that captures directional stiffness, auxetic kinematics, and pressure-sensitive plasticity. The model is implemented in ABAQUS® via a user-defined material subroutine (UMAT) and validated against experimental results across multiple loading paths. The proposed workflow demonstrates a closed-loop multiscale strategy in which experiments inform numerical modeling, simulations support experimental interpretation and design, and both domains mutually enrich each other. The framework contributes to modern paradigms such as virtual testing, simulation-driven experimental planning, and data-informed constitutive modeling for complex architectured materials.