Hey I've almost completed the game, I've unlocked green pipes point, so..

Some advice on those nollies:
1. For the first one, just go reasonably fast at the ramp
2. For this one, grind the ledge on the right of the starting place, then jump just before it turns, so that you hit the wall, turn a bit and land on top of the ledge. Get into nollie, and the speed you just got from the grind should be enough to help you hardflip the gap
3. Use focus for this one. Press the directional buttons for the smallest amount of time possible when doing the hardflip, so you don't turn too much in the air. Land in a manual, and the rest is easy.
4. Again use focus. Skate back a bit to get a big run up, then pop your nollie on the corner of the ramp, going over the street. Triple heelflip in the air and land on the ramp in the street. All you need is speed.
5. Just time the boned ollie just right, and hold [x] in the air. In fact, land while holding [x]. Try and figure out which bit of the ramp is closest to the roof you're landing on, and try the boned ollie from there.

Hope I helped

My brother taught me this. On 3 you just do the nollie triple heelflip off the kicker then try to land a grind on the power line and then get close to the ramp and bank drop onto it. This helps if you don't have many speed or air stats.