Everyone does this different, I would suggest what SLP said, set it close like that. It's what I call pickup clearance. Think of it like a stick shift car. the closer the clearance the more graceful it will engage the belt. Big gap will hit hard, and if your motor can't pull it, it will bog. However, you need to have your secondary properly adjusted for belt tension as well.
The Spider washers will adjust this, this won't change engagement RPM, just the way it starts to apply pressure to the belt. This also change the entire shift curve to a certain degree. Get this aspect worked out and then you can move on too Full shift RPM, over rev, and back shift. Racing is going to suck if you can't get off the line.
Too much to explain in one post in my opinion. Sounds like your starting with no past history to work from, so in my opinion you need to work with an experienced clutch tuner, or as others have said, buy a lot of components and test, test, test.
At minimum you need a gram scale, a pull scale for the secondary, and spring tension tester to evaluate idle and full full shift primary spring tension. No two springs are the same.
Also, keep in mind the level of traction you have and gearing will also play into what works.
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