I think you'll struggle with 17's.
It'll need major arch cutting.
Riclemus might be able to help though, he's just fitted 50mm springs on his HGT with 17's.
i got 50mm gmax springs in my bravo hgt (wider arches than standard bravo). i have only got the front ones in but they fit perfectly, no arch rubbing at all and i still get sull lock on the steering. the back ones will need a bit of arch rolling but thats nothing a hammer cant sort out! beware spring compressors if ure fitting them ureself because i nearly broke my fingers when a compressor exploded from full compression taking my hand and knee with it. care is not a joke! seriously tho i wouldnt go lower than 50mm. my ride now is ****, the engine plastic guard scrapes on everything and i cant even look at a track or lane, pebbles in the road scrape. all manner of crap gets stuck in the engine bay. u get the idea. i have a set of 35mm springs as well so i might put them in the rear because i have such a huge weight of ice in the back its already lower!
The best is to use Eibach, Sparco or OMP with 30mm lowering. I am using B&G coils, about 40mm lowered with 205/45R16 tyres. Rear part, no problem, but front part, rubbing the inner plastic cover wheel arch, if riding hard on a bumppy road. So, the best is to go for 30mm and you will be saved.
I am using Coupe 16" 20VT rims with 205/45R16 tyres. I have to changed back to original springs at the front to avoid wheel touching the arch. But at the back still maintain the lowered springs. Comfort wise, the same. Maybe because the KONI shocks doing its bests.