The spur gears are custom, hand made for the car, hence the expense. The one on my car is the original one from the start of the 2007 season. I have been meshing mine properly though
Slipper setting is up to you. Best is to let it slip just a fraction on take off from a standing start on a surface of reasonable grip, this will then protect the rest of the tranny.
I had to laugh slightly at your comment that someones said to have it tight to protect the pucks as the pucks are the very component designed to wear out and so are the consumable components. If you're protecting those, it's too tight and so will pass the strain onto all the other tranny items so expect to go through drive and diff pulleys and belts MUCH more often than you would otherwise. The front diff and drive pulleys in my car are also originals from the start of the year in my car, I did preventativy change the rear one when I had the rear diff out last, so have used 2 all year.