Hello and welcome Matty. I have a TR GTi too. Great choice
Personally, I would leave the Monza II as they are, look much better and if you ever want to sell they will be worth more as originals.
Carbonio intakes are useless, save your money. They just look pretty.
Go for a CAI kit like ITG, Evoms or Forge Twintake (I have one of these). Will give you much bugger gains and sound better too.
Rather than searching for an ED30 splitter (which is almost impossible to find second hand) why not buy a Votex front lip from VW direct. Looks slightly better and is a much less common.
Of course, this is all just my opinion. You have no obligation to take heed
Apart from that, enjoy your car and test out the launch control