Guys, Keep it simple and correct:
1) V1 is Thrust related so depends on your density and temperature (thus also your flex. tmp. calculations)
2) Vr and V2 are always MASS related and are the same for a certain Take-off Mass. They do not change unless your payload or fuel changes.
3) Your MTOM depends Runway length and condition (think contamination or up/downslope), ambient temperature and density.