The 225 isn't the best base for big power as you might think. It's a good base if you want to keep it sensible ie, below 300bhp.
The code should of been AUQ as there wasn't a AQU code

The 150 lump with AGU is the best one. It has larger ports on the head. Even though the bottom end's are pretty much the same you'll be changing pistons and rods (I hope) when you up the power.
150 engines have a k03 - good for 210bhp (220bhp max)
180 engines have a k03s - good for 225bhp (240bhp max)
210/225 engines have a k04 - good for 280bhp (300bhp max)
The first power is safe and reliable. the 2nd can be achieved, but turbo life is reduced.
As for the engine management... The OE management is good and reliable as we know from all the mk4's, A3's, TT's, etc on our roads today, but is plauged by the worst invention ever - the MAF. Most standalone management systems such as DTA, Emerald, Motec use their own boost map sensors which are a lot more reliable. The OE management monitors the engine in pretty much every place it can and has knock sensors so the management will rescue the engine if you're pinking or running lean to save blowing holes in pistons. Some of the standalone systems don't monitor the knock while means you can get that little bit more bhp from them as the OE will always fight for the side of reliabilty over raw power.
You will pretty much need the management remapped once it's all on the car and running to take into account that non-cat exhaust and free flowing intake. they can also adjust fueling and boost levels to bring the bhp up. The standalone setups will defiently require a map as the base one just about gets the car running and it's not advisable to drive too much on that.
I just paid £450 for a DTA ECU, I'll need a loom which are £305+vat from Stealth, a map sensor £50 and then Vince's time spent mapping my car at Stealth - another £400-500. That's gonna bump up your budget a lot!
I've written enough now
