White smoke is usually attributed to:
1)Coolant burning from a leaking head or intake gasket (suggested by Toadie)
2)Normal carbon buildup in the motor
3)Turbo seal (suggested by salvageV6)
4)Cracked head (worst case scenario
)
Backfiring is normally a plug, coilpack, or ignition module problem I believe. Someone can correct me on this if I'm wrong. What plugs did you use? Gap? What maf?
A coolant pressure check may be a good place to start. You may consider pulling the plugs one by one after warming up the car & look for any steam coming from the plug holes. Evidence of this could possibly be a leak in that particular cylinder. A compression check may be done at the same time.
Have you been able to purchase a scan tool yet? The readings from them can really help you when diagnosing problems & tuning the car. Let us know.