Could someone explain few things to me, as they are not 100% clear to me

1) If I challange someone and lost do i lost all my trophies or only the one we are playing for?

2) And If I beat someone did I gain all his trophies or only this one new?

3) So what are the best tactics for this event? I see that you can play 1 time against everyone, so play as much games as early as possible and in last minutes make last challange to someone?