Exhaust and Header?

Hello fellow experienced WRRers!
I am a mechanical beginner and I have a couple of technical questions:

When considering changing the stock exhaust, does the header need to be changed too? what are the pros and cons of changing the header or not changing the header when changing the stock exhaust? I am thinking of FMF Q4.

From what I've been reading, the following main modifications complement each other.

In what order should these be done ?

Fuel programmer
Open the airbox
Change exhaust (header too?)
Servo sub
Ais removal

All of these should be done?

Thanks!

The pros of installing a fmf head pipe are a little more top end hp for the powerbomb and little more lowend tq for the megabomb, both make the bike a touch quieter too.
The cons are they're not a good bang for your buck, they cost a lot and only add a little power at the very top or very bottom where you don't spend much time while riding.

IMO its best to do a pipe, programmer, air box mod and AIS delete at the same time, you get the most hp and best rideability this way.

I simply unhooked the exup cables from the servo motor instead of spending money on a servo delete.
If you don't get rid of the AIS you will get back firing when you let off the gas, it doenst hurt anything if you can stand the racket.