3" DP

Hey im a new user as well.....tryin to figure out good starter stuff....whats a good cheap DP, Throttle body spacer for zex kit, and O2 sensor.......are these ne good.....and why is there an O2 sensor spot on this DP wen i would get a O2 delete.....

Downpipe
http://www.3800performance.com/Merchant2...roduct_Count=23

O2 Sensor
http://www.3800performance.com/Merchant2...roduct_Count=17

Throttle Body Spacer(Zex)
http://www.3800performance.com/Merchant2...Product_Count=4

All good products,and I'm using that TB spacer now with a ZEX kit with good results ,as far as the hole in the DP just plug it with a bolt .Chico.