The Stagea is a very nice car but was quite rare a few years ago and whilst the running gear is largely skyline the panels might prove a problem to find. So don't dent it!
I was at Surrey Rolling road a year or so ago and there was a 560hp one there. Running gear is supposedly very strong but upgrades to power can be expensive. Doing things on the cheap with japanese cars can be a false economy.
Just don't start upgrading it without the right people doing it right as it will cost a fortune!
Perhaps not the most nimble thing out there but definately a q car.
I would be looking at a merc c43 Amg If I wanted to keep the costs relatively low and also retain some comfort.
That said I was at Spa a few years ago and there was a Stagea there and it was flying.