I don't know if they'll be really good friends considering what Korra is doing and how Bolin is oblivious to it. Asami's reaction is understandable. It never would have happened if he didn't dig his nose in that.

I don't think it was anything against the sport, just against benders. Pro-bending distracted the citizens and made it seem like everything was normal, which Amon was against. Pro-benders are the closest things to bending celebrities in that city, so destroying the sport by making those he missed not want to play anymore and hide seems exactly what he would want. 

It depends on where Asami and Mako were at the time. If they were at the arena, then the event becomes larger on the scale. If they were on a date, then they just hear about it, maybe see the Zeppelin from wherever they're chilling.