Unity 3D Game Developer(Urgent Job)

I want to reskin and add simple functionality to racing game. I have source code of this game. The game is in Unity 3D format. I want to implements: 1) Change some graphics and Sounds. (I'll provide all designs and sounds to change) 2) Add 3 power ups - Invincibility item: It lets the user not lose time even if the car hits the other cars. (It has been completed but have some bug) - Repellability item: makes other cars move away from the player. - Coin Magnet: player attracts all visible coins. 3) Coins collected can be used to buy any of the 3 power ups. Player can also buy additional coins through in-app purchase. Thanks.