>If you run over a switch on the first lap, do you have to hit it again on the following laps?
Sometimes yes. Sometimes no. If I remember right, most switches only need to be hit once (hitting it a second time will switch it off). Immediately off the top of my head, the only ones I remember that do need to be hit every lap are those on Track 2 (they automatically switch themselves off after some time).
>Can the coins be collected in any mode? (trial, circuit, etc) I'm trying to unlock a car.
Pretty sure, yes. I always did it in Practice mode.
>What is everyone's favorite car?
I like the Locust and Euro, but my favorites are probably the Formula 1 and Super GT (both of which aren't ones that need unlocking). Unfortunately there's not that much difference between the cars in 2049; not like there was in the 2 previous Rush games anyway. It's mostly just aesthetic and slight handling differences this time.