Welcome you have lots of plans so start saving its going to be a life of spending and smiling.
You need to get some very good rubber, lots of threads on here about what is best but if you start mapping you have to have them to keep the car on the road.
I have the maxton front and side skirts and they are great, not in your face but look nice, Just seen the rear diffuser and saving to get that one myself.
With regards to stage one, Revo also do a nice one and will be offering a discount soon (last year it was black friday and they gave 25% off), APR just did there discount so it will be a while before the next one.
A few things that add to the car in my opinion are Gas Bonet struts and upgraded Boot Gas Struts so that you can remote open the boot, looks cool and also practical.
You also need to check out OBD11, VCDS Or Carista so that you can make changes to the way your car works.
Enjoy you have got a great car.