Just a couple of tips to help speed the 100% achievements for this game up.
From the main menu you will be playing through the highscore run game mode. When you load into a game you are on a timer with three challenges you need to complete which vary in length and difficulty. You receive credits at the end of a run for each completed challenge which go towards purchasing upgrades and new maps. There are 4 additional maps to purchase each costing 2000 credits each. I would also recommend fully upgrading a vehicle for some of the later challenges in the game.
Once fully upgraded and maps purchased you will not need to end a run if you have completed a challenge to register it as complete as the xbox tracker will go up as soon as the challenge completes, so if you wish you can press start and click restart run rather than waiting for the in game timer to reach zero each time. You will NOT receive credits for the completion of the challenges if you do this just progress towards the achievement so I would suggest doing this only after you have purchased everything you need.
At the start of each run if you did not complete a challenge in your previous run you have the option to skip a challenge for a small amount of credits, which is worthwhile if you are struggling which a particular one.
As for the vehicle of choice the starting vehicle red fury is more than enough fully upgraded but there are other contenders you will unlock as you progress. The MVP 48 (formula 1 looking car) is my vehicle of choice which you unlock as part of getting the 10 million point achievement as it is extremely fast and doesn't bounce around as much after landing a jump.
If there are any other tips feel free to comment and i'll add them on here. Good Luck :)