I wouldn't bother with the coil pack la. Unless you want to buy new? Used one you don't know how much life left in them and there's two types of K20 coils, both of which are expensive. If you insist on changing COP, consider the 1NZ (Vios) one. It's much cheaper and plenty of available stock.
A remap even without a COP change will make a difference and then depending on the age of your stock COP, even a brand new Jazz COP swap will make a difference if the old one is worn out (maybe past 200k km?) My Myvi made a difference after I changed the COP out to OEM coils after 10 years of using this Myvi and 200k++ km mileage.
Ya, downpipe is from the header to the catcon. You removed the catcon?