As for the second one, it took me a bit to get that one too (and I had to use the trainer to get it). In the upper right corner where it tells you how many fans you've got there's a number to the right of the fan symbol. That's your multiplier. The heart fills up and the multiplier increases by 1x when you do something to add fans (hit someone with a powerup, drift, nitro etc..)
After you do something, the heart starts emptying. You need to do another something to add more fans before the heart empties and it will increase your multiplier.
I was fighting to get this one a lot, so I just turned on unlimited powerups, picked up a bolt and blasted the heck out of everyone at the beginning of the race. Every bolt hit increases the multiplier by 1x, so it didn't take much time. Then I turned it off and went on and won the race. I don't know if coming in 2nd or 3rd completes it because I got first.
Sorry for the length, but I hope it helps
They are tough, and they go higher
Unfortunately, a lot of times its hit and miss. I usually try to go for winning the race first and then on replays try to hit the fan targets.
Doing the Fan Runs helps, and also try and stay with the pack, or at least have some cars around you to beat up on.
I haven't had any that I've had a real hard time hitting yet, but I've had to retry some events to hit the number. The good thing is that I haven't had one yet where I've felt it was impossible to get.
as for the big fan number you have to get if you know how to play this game you can get even with +300 fans than the min requirement...that's what i did :P