Before embarking on your upgrade journey, there are a number of OEM factory parts that may be worth refreshing.
Diverter Valve (DV):
There have been several revisions of the factory diverter valve. The latest (which I'm using) being G. I have on several occasions considered a DV+ and whilst some swear by it, I've read stories about them needing maintenance every 6 months or so to keep them going. For the price of a DV+ I could buy 3 OEM DVs anyway. Also, from my research, any kind of aftermarket dump valve is usually removed pretty quickly and definately isn't a requirement.
Again, the factory PCV can be a weak point. The latest revision is R and doesn't cost a whole load of cash to replace. It also usually comes with a new gasket as well.
DV Return Hose:
I include this because shortly after going Stage 1, mine started to give up. So I replaced it with a snazzy Forge silicone hose. But note that Revo have since moved the location of the DV return connection so it was a real stretch (literally) to get it to fit. I'm not exactly 100% pleased, but what can I do?
The destroyer of engines. This tiny thimble size component is a particular weak point of the TFSI engine. Personally, for the price it's worth changing at every service. At 2+ it's advised to check it every 5k miles.
RS4 Return Valve:
The fuel return valve opens when the fuel pressure reaches a set value (127 bar I think). This was a problem with Stage 2 onwards because rumour had it the Revo maps requested 130 bar at their peak. So for 2/2+ it's recommended to go with the RS4 valve (135 bar).
Ah, not a day goes by without a "is premium fuel worth it?". My personal opinion is that putting premium fuel in an engine expecting 95 octane will at best clean it a little if it's filthy. It won't magically give extra BHP. The purpose of higher octane fuel is to avoid engine knock. If your going for a map, put V-Power or Momentum 99 in or you'll be greatly disappointed.
I debated putting tyres in the performance section. But, if you've gone to the time and expense of modifying a car to circa 380bhp, tyres are an essential not an upgrade. At Stage 2+ expect to wheel spin, a lot. And no mod short of 4WD modification will prevent this. Before someone jumps in, a limited slip differential will help going round corners, but is effectively "off" in a straight line. But with careful application of accelerator and decent tyres, the occurences of this can be minimised. If money was no option, I'd go Pilot Sport 4 every time. However, if on a budget my personal recommendation is Rainsport 3. If its tanking it of rain especially, be prepered to lay off the happy pedal.
Up to Stage 2+, I used 5W30 Castrol Edge. It's perfectly normal for these engines to "use" up oil in normal operation. I was topping up from just over min to the max mark once a month. So I switched to 5W40 (as the engines now running hotter) and now do the same top up around every 2 months. This will of course depend on mileage and usage may vary. I use Millers NT+ because nothing says I love you to your car than buying really expensive oil. But in the words of a recovery vehicle operator "any oil is better than no oil". < Ask me how I know.
I spent months researching online trying to decide whether to go Platinum (PFR7S8EG (1675)) or Iridium (NGK-BKR7EIX). In the end I went with "if it ain't broke don't fix it". As far as I can tell, there should be no discernible performance difference between platinum and iridium. But note that there may be a big difference between plugs that have done 100k and any new plugs. Basically Iridium lasts longer at higher temperatures. But as my car is running great on Platinum, I chose to keep with the Platinum and change them more often if needs be. At £30 a pack, once every other year is hardly going to break the bank.
Red are best right? Well, technically, although the resistance is different to the OEM packs. There's no evidence to show that the red coil packs work any better or produce more bhp over the OEM packs. But also worth considering that new coils may produce a couple of extra bhp over 10 year old coils with 100k on them. However, that said, as will all mods: anything red (including decals, body pieces or aftermarket parts) adds at least 20bhp (Disclaimer - they really don't). So I got them anyway.
Probably also worth mentioning at this point, if you've removed your engine cover (which if you have an intake you probably have). Keep an eye on cylinders 1 & 4 as they tend to get water in them. This can cause the coil to rust, and if you have the red ones, you'll likely be splashing out on four new ones.
If your asking yourself "Do I need a new cambelt"? The answer is probably yes!
Do I need a new cambelt? No, no I don't. I had mine done last year. It didn't "need" doing, but as I didn't know the history of the car circa £300 now should save me circa £3000 later. If I recall, it has changed several times from the owners manual, but I believe it's now 4 years or 60k miles. And yes you should do the tensioner and yes you should do the waterpump if your doing the cambelt. I believe Seat offer a 5 year warranty on new cambelts and Indys 2 years. So make sure to do your homework first.