1. Its cheaper and easier for Audi to make one shape front bumper in SE, Sline and S5, so that they fit the A5 bonnet and wings. Otherwise they would have to make a ton of different wings & bonnets for each trim level
2. I put an s3 front bumper on my A3 sport
3. I plan to do this mod myself, albeit on a facelift, but its the same principle. You can see how it transpires but you'll have to wait till October.