ApocalypitcNinja is right you can use Metal from the cars for a quicker build resource. Personally I'd like to make the game more difficult so I am planning on adding a difficulty slider that will allow you to change the difficulty however much you would like.
Also for multiplayer it really slows down the whole process so the goal is to just do couch co-op for now untill release on the PlayStation in May which is the dream.
Hope this helps! Thanks for the feedback and support, lots more coming very soon,