Adaptive cruise control

This should not be a problem at all. As you can see the grill (for example from an Tit S) with ACC cover has nothing special:

It is more to prevent dirt and stone hits from the radar unit itself. If you place a plastic behind the grill yourself, it should do, Optics is another story, though

I depends. You may look at the Chinese market. There are cheap replacements in good quality. And, by the way, the grill is the almost cheapest part if ACC...