Mario Kart free roam mode?

So been playing some MKW free roam a bit but I have a question or 2, like does activating those “?” panels you run over actually do something at all other than just getting some stickers and same with what do the Peach coins do because I think it said something after I got my third one I just didn’t understand what it was?

Also driving around I came across Nabbit twice now and caught him, I got a sticker the first time but I don’t think I got anything the second? So is there a point to keep trying to catch him again or do I have to keep going after him to and catch him a certainly amount of times for something else to happen??? Thanks.