Welcome to the site.
It might be worth posting up a photo or two of the engine bay; if it's been played with under there you'll want to know everything is as it should be. Aftermarket parts can often be a downgrade if not done properly.
As for lowering, unless you want to go really low, H&R springs are a nice option. They work well with the standard dampers and give quite a nice stance for springs. Only caveat is that they will wear your dampers faster than running the car at standard height. Ideally you'd fit some uprated dampers at the same time; Bilstein and VWR are decent options.
I'm not sure what options you have for mapping over there but if you're staying at Stage 1 for now Revo are good generic option.
In the meantime do a bit of reading up on the basics, and importantly, get these sorted before you think about tuning and lowering:
Cam follower
DV
PCV
There are loads of threads on the subject. I'd recommend the oem Revision G DV and oem Revision R PCV. These parts are deemed good for the life of the vehicle by VW, yet over time it's become clear they can and do fail. Arguably the most important is the cam follower - if these wear too much you're looking at a damaged camshaft, damaged fuel pump, and big bills. The DV (diverter valve) can split, losing you precious boost. And if the PCV fails your car will run rough - bad idle etc. Another part that doesn't form part of a service is the fuel filter. It's not a big job and worth doing for peace of mind.
Use 5w40 oil. Standard Bosch spark plugs are good. Coilpacks often fail, giving misfires under load - over here a lot of us fit oem Audi R8 coilpacks. They're essentially identical to the black GTI coils, but a bit cheaper, and red!
And if you have the option, run it on the highest octane fuel you can buy.
