Stock rims will work. But i'd get set of 16" wheels anyway. At least my choice of tires costed 150eur less for set of 16" tires vs 17" ones.
As i didn't tracked this winter, just daily driven it, there wasn't much problems with ice/snow getting between spokes/causing imbalance. Funnily, i got that effect when already changed to R17 wheels/summer wheels, on 2nd trackday day of this spring. Car spun out of track, left rear wheel got thrown in lot of earth/dirt inside. After driving further seemed that's it, something broke in suspension .. nah, just dirt debalancing wheel causing it to vibrate when driving. Quick brushing off and track day could be continued
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BTW - while lesser count of spokes makes easier for dirt (/snow/ice) to get in .. it also makes it easier to clean out with all that open space between spokes (6 in my wheels). Have some doubt on ease of cleaning steelies, with all the closed space with many very small openings at best.
Also it was interesting to find out, that local rally drivers often make/use some inside wheel ice-scrapers, & attach those to brake calipers (or rear arms?), to clean up wheel inside when driving. Will see, maybe worth ordering such. IF issue of snow/ice inside wheel appears often enough to care.