as you said, just loosen off the 13mm bolt, knock it up the adjuster and the belt will come off. There is absolutely no need to remove pulleys or take the alternator belt off. Although it is worth doing it as you are down there.
can't remember off the top of my head how long the belt is, but what ones do you have? The numbers usually refer to the length. i.e. 800 = 800mm
There should be enough adjustment on the pump to tighten it up.