Yes OEM body kit is much less prone to scraping than these aftermarket. You can from the shape yourself. My car has scraped its belly countless times, but never ever got even close to having the bodykit damaged.
As for tires, here's the options:
1) Conti MC5 - more sports oriented
2) Conti UC6 - less sports, more comfort relatively (CC6 is most comfort oriented, and UC sits between CC and MC)
3) My fav Yoko Advan dB
I'd be surprised if even Conti CC beats Yoko Advan dB in terms of quietness. Problem is that Yoko V552 has just arrived (V551 is older model now). So most V552 is currently smuggled and much more expensive than Contis, from what I've asked around.
Currently I'm running Yoko Advan dB V551 215/45R17, but if I change them I might go for 215/50R17. This is because firstly, 215/45 is hardly available in the market now, secondly, while these Yokos are definitely soft, 45 sidewall is too small to absorb bumps. Thirdly, even though I'm very much against increasing tire size, but 215/50 being ever so slightly taller, would give me a bit more ground clearance.