The very first stages of the non-diffusive growth of Mn5Ge3 thin films on Ge(111) substrates are characterized by several techniques. Mn5Ge3 films are grown by molecular beam epitaxy using the co-deposition of Mn and Ge atoms at room temperature. XRD measurements demonstrate that the thin films are monocrystalline. The evolution of the RHEED intensity during the deposition and the AFM images show a step-flow growth mode. RHEED patterns, combined with TEM images, prove that the lattice mismatch of 3.7% is accommodated by the formation of an array of interfacial dislocations and by the presence of a residual strain in the thin films. These observations are supported by the numerical calculations of the critical nucleation volumes exhibiting very similar values, in the case of a pseudomorphic growth or in the case of an accommodation of the lattice mis-match by interfacial dislocations. Furthermore, the effect Ge/Mn stoichiometric and Mn-rich fluxes on the surface morphology is examined.