handling car 17's or 15's?

If you're going for handling, you should keep your considerations to 17's or 18s. Personally, if I had the coin, I would go 18s. Might be a bit more going in, but if you do suspension or brake upgrades later, you don't have to worry too much about whether the wheels will clear or not. Trust me, if you're building a handling car, there will always be upgrades....