i recently purchased the bracket , rotors, and pad. I notice i am missing the small backing plate for the bigger pads. Do i really need them? What's their function? By the way, i got the whole set of rotors with pbr ultimate pads for 200. Too bad the rotors r slotted and crossed drilled, hope they don't crap out on me.

 

The backing plate is to keep the noise down, not a biggie IMO.
If you don't push your car too much you will be ok, I found that slotted/drilled rotors are nothing better than regular rotors when it comes to overheating them. If you plan to track your car, it may be wise to get non-drilled rotors before your track day.