The ISS can be refueled with UDMH and N2O4 by visiting vehicles, initially the ATV:
The propellant transfer is done through the docking connector, through pipes that run outside the pressurized portions of the ISS.
The difference in loading a flown booster and a brand new booster is the same. SpaceX starts loading RP1 and first stage LOX at T-35 min. RP1 fueling on the first stage finishes around the T-3 min and second stage around T-2 min time. For LOX fueling, they never really finish loading, they will keep topping off the LOX that's boiled off til about liftoff. So ...