Wise words indeed..... 350 hp is all well & good, but you need to be able to get the power down!Its a tricky one i know, but think of it this way, a K03s is an inexpensive stepping stone if you do happen to find its not enough power for you.
All i know is i went to the Nurburging with a group of friends and one had a Mk4 1.8t, it couldnt of been running much more than 200hp on standard K03 and could easily keep up with everyone if not beat them, including a bmw m3 and a 280hp r32, and lots of porsches, he had sorted his suspension and it handled very well, its not all about power, you need some power and a standard 150hp is not enough for the mk4 golf, maybe 230hp might just cut it, with a properly setup car, if not move on for bigger things.
350hp without some assistance is going to be very difficult to use anyway i would imagine, all depends how much cash your willing to spend.
Depends how much you want to spend... I'm going down this route at the moment. KO4 turbo and manifold with the water and oil pipes £500, bigger injectors £100. Total cost for this to be fitted and mapped with a full turbo back exhaust looking at £1600. Its being done at PSI tuning, Andy has a corrado in there with near enough exactly the same spec and this rr at 292bhp. When I get mine back I will let you know what it produces.the ko3s is 125 from breakers and i will be taking of my self so i will be takeing the lot intake pipes etc but i was also considering a ko4 but not sure on how much it going to cost