You don't need a downpipe for stage 2, testpipe + catback and you're good to go. Hell I ran stage 2 on a completely stock car with no issues

Give it a go

 

I'm not going to risk my car for just little bit of more power.

I have something wired after installing AP, When turning the car off and twist the key to off position I notice all the lights comes on for a sudden just like when you reflashing the ECU, Do I have to resset the AP or something?

 

He's right about Stage 2,

I'm running it with the stock DP (I've got a test-pipe and cat-back) and my AF levels are more than fine...