It's normally recommended to have 2 leaves for soft top vehicles, 3 for hard working truck cabs/lots of towing for example, 4 is really for 109s only.
But as said above you do get a good variance between manufacturers, and shocks too, you may find cheaper ones with less damping suit your needs better, but it could all get rather expensive if you keep having to swap them out...
You can get polybushes for the chassis separately, just took some googling... I replaced mine recently with these:
http://www.island-4x4.co.uk/polyurethane-bush-black-britpart-569746py-p-6318.html
I know it's sh!tpart, but what's better, a bush that waggles about in the hole now, or one that might waggle in a couple of years or so -it's on a low mileage truck.