If you do it with #4 at TDC, then you actually have a mark that you can reference, when lining up the cam pulley (there is a mark on that black plate that sits behind the cam pulley). If you do it with #1 at TDC, then all you can do is try to line up the cam pulley mark with the crank pulley mark (not a real precise way to do it, especially for someone not familiar with lining up the marks).
I'd suggest doing with #4 at TDC, just because the marks are easier to line up, if you happen to move the cam.
You do have to remove the cam pulley and the crank pulley to access the seals behind them. So there is a good possibility that the cam and crank will move a little, when you try to remove the bolts that hold the pulleys on. So you will have to line up the pulley marks with the reference marks, before you put the new timing belt on.