Few things I picked up on whilst playing
I repeated the big finish style event till I could buy the mantra (highest top speed boost compensated the lesser acceleration)
You can't always unlock 3 stars first as the game rubber bands oppenents a lot.
When In. racing or elimination mode don't hit every jump the landing will cause a bounce for you and the AI that will slow you down if you go to side you will fly past opponents,
If you have 3/4 or more boost you shouldn't take any jumps.
If your boosting whilst turning and can't make the turn let go of the right trigger, you don't slow down but you gain more control atleast most of the time, if your In group the other racers waves can push you out into walls.
Always save some boost for the final stretch the AI does the same and 2 seconds from the line you can go from first to third.
Freestyle maps try to use you biggest point move over and over till it's worth as much as you next biggest move and work you way down table turn move (rotating horizontally) can make you land side and lose speed so leave this till last or when you sure you can make the landing, if you boost before a jump and hit it dead on you will get enough time to land a lvl 10 trick.
Not a whole lot else to add it isn't horrificly hard, I dislike racers and am bad at them but I just 1kd this game. I'd say about 6-10hr to finish depending on your skill level.