The only real difference between one, two and three disks is the amount of disk surface used to lock up the clutch. In theory the additional surface will allow the clutch to be used depending on how you want to look at it, with higher hp or torque. The important thing with any clutch one, two or three disk is that you cause it to lock up at a particular rpm, usually at peak torque or around peak torque depending on the opinion of who you ask. It probably will work fine.
Tell us what color the springs are and someone on here should be able to tell you the range of rpm it's designed to lockup at. I have not looked but I think the rpm engagement rpm for different colored springs can be found on Buller's web site. Or I'm mistaken about there being different color springs of different tension, that can be used in the same clutch.
Agree with earl, you need a 2 disc for what your wanting to run. Rule i use is, single disc for juniors, 2 disc for adult unrestricted classes, and 3 disc for limited/open classes.
you shouldnt have any problem trading the 3 disc bully for a brand new 2 disc bully if you post it in the classifieds on this site, or talk to one of the clutch guys like Ryan Thompson, Martinbuilt, or Jammer.
i dont know about wearing the clutch out quicker but if you have it set to engage too soon before peak torque then yes it can bog your engine down and kill you on the starts and restarts. the only thing i can see wearing the clutch out sooner than normal would be if you have it set to where it is slipping alot, such as if you have the engagement set too high and are constantly engaging and disengaging the clutch as you go thru the corners. Or holding the brake and throttle at the same time would also cause the clutch to wear quicker.