Wheel option for Polo GTI

[GTI JOE]

Probably been done to death but here goes.

Polo GTI (6R) stock wheels and tyres are 17X7, 5X100, Offset 46, 215/40/17. Now, I have H&R springs installed (25/40). Interested to know if it be possible to mount 18X8, 5X100, Offset 45, 225/35/18? Any opinions on performance, legalities, stance etc.????