Molecular Dynamics Simulations in VASP

I want to run molecular dynamics (MD) simulations with VASP for Mg2Si to investigate the simulation time vs ENCUT and KPOINTS, but I do not know how to set INCAR tags for example for the first run if ENCUT = 500 eV with 100fs time then should I change the value of ENCUT and time for the second run? What parameters of INCAR will remain the same to compare ENCUT with simulation time and to get one plot of energy convergence? If the first run goes well should I change my POSCAR too for the second run as input?

Thanks.