Do not listen to the chief especially for boost because you might need it for shield and you might lose concentration because people complain of crashing and bumping well the sure is going to be helping you on that.
How To Get Unlockables
If you want to get an accessory or a car part that an opponent has, go to a race were you are racing the opponent, then unlock one of the career goals and in 1st, 2nd, or 3rd goal you should get it, if you don't get it there are other races that have the opponent so try it on another race.
In an online race you can get extra xp you can press O for shield then drift while sideswiping. Another is to get boost weapon and jump X X and square to boost jump at the end.
If you lose a race online you will lose a lot more points than how many points you get winning. Racing online is tough.
When you are creating a car remember that bigger and squarer the harder it will be to do spins but easier to sidswipe and stomp.