High-entropy MAB (HE-MAB) phases represent an emerging class of layered boride ceramics with exceptional potential for high-temperature structural applications, yet their thermodynamic stability and atomic-scale ordering mechanisms remain incompletely understood. This study employs density functional theory calculations combined with the special quasirandom structure methodology to systematically investigate the stability, electronic structure, and chemical ordering behavior of binary, ternary, and high-entropy Cr-based M₄AlB₄ compositions. Convex hull analysis reveals that all three investigated five-element HE-MAB phases achieve thermodynamic stability at 0 K, demonstrating that configurational entropy can stabilize phases that remain metastable in lower-order analogues. Temperature-dependent Gibbs free energy analysis establishes that all metastable compositions become thermodynamically accessible well below typical synthesis temperatures, with critical temperatures ranging from 83 K to 663 K. Valence electron concentration emerges as a key descriptor, with an optimal stability window of VEC ≈ 5.5–6.0 identified from divergent parabolic trends in thermodynamic stability and formation energy. Atomic size mismatch analysis quantifies a linear stability penalty of ΔH ≈ 6.5δ meV/atom per percent mismatch, with entropic compensation effective up to δ ≈ 9%. Short-range order and sublattice site preference analyses further reveal that elemental self-organization constitutes a complementary enthalpic stabilization mechanism alongside configurational entropy. These results establish a multi-descriptor framework providing quantitative guidelines for the targeted synthesis of stable HE-MAB phases.