Recent transport experiments in rhombohedral multilayer graphene have reported evidence for metallic Wigner crystals (mWCs), characterized by the coexistence of crystalline order and a small density of hole-like carriers. This coexistence raises fundamental questions about the stability of mWCs and the fate of their collective excitations in the presence of gapless fermions. Using self-consistent Hartree-Fock and time-dependent Hartree-Fock calculations, we demonstrate that itinerant carriers profoundly influence both. We find that mWCs with electron pockets are generally unstable to particle-hole fluctuations, while hole-doped mWCs at lower densities remain locally stable. In the stable hole-doped mWC, the longitudinal phonon strongly hybridizes with particle-hole excitations, while the transverse phonon remains relatively well defined. Quasiparticle coupling is strongly mode-dependent and is typically stronger for longitudinal-like excitations than for transverse modes. Our results demonstrate that self-doped carriers not only enable metallicity but also fundamentally reshape the stability, collective dynamics, and quasiparticle interactions of electronic crystals.