The PFL car has a smaller turbo than the facelift model which limits power to a SAFE level of tune for Stage 2 on 99RON at around 450ps and up to 700nm (MRC and APR tunes, but REVO torque is much lower). In my opinion the addition of a downpipe on the PFL car is not an essential item as it does not really provide the expected benefits versus the cost of buying and installation, again it's the stock turbo which is the limiting factor as it's pretty much all done at 450/460ps. You can coax some extra from it by mapping the car to run on race fuel, but I have only seen cars running at around 475/480ps that have had air intake, downpipe, IC and a host of other mods to accommodate the race fuel tune.
The addition of an uprated IC is highly recommended as the PFL RS3 suffers from heat soak after some hard pulls (as does the brakes lol) and the ECU will pull power to protect the engine from rising temps (seen as much as 40 to 50ps drop on heat soaked cars on dyno runs). Intakes can be hit and miss (the fancy carbon ones work better with a turbo upgrade) but a larger air intake pipe like the Forge or HG Motorsport and a panel filter (BMC or K&N) can help the engine to release a few extra ponies and torque without breaking the bank for the carbon fibre look.