We present an in-depth multi-scale analysis of the conformations and dynamics of polar active polymers, comparing very dilute and very dense conditions. We unveil characteristic length and time scales, common to both dilute and dense systems, that recapitulate the conformational and dynamical properties of these active polymers upon varying both the polymer size and the strength of the activity. Specifically, we find that a correlation (or looping) length characterises the polymer conformations and the monomer dynamics. Instead, the dynamics of the center of mass can be fully characterised by the end-to-end mean-square distance and by the associated relaxation time. As such, we show that the dynamics in melts of polar active polymers are not controlled by entanglements but only by the strength of the self-propulsion.