You answered your own question.
He will be 18, he works, he will be an adult. It is time to tell him to man up or move out.
If he does not want to pay for the car insurance, then take the keys away - it is your car - it is his privilege to use it, not his right.
Charge him rent, have him sign a lease agreement - he rents a room in your house with bathroom and kitchen privileges, and three prepared meals a week. He contributes $ to rent, $ to groceries. Reserve fridge and freezer space for his food that he will have to buy with his own money. Give him a schedule of when he is able to use the kitchen that doesn't interfere with your meal prep time. If he doesn't clean up, charge him a surcharge for house keeping that week. Keep a ledger account of his charges. If he doesn't pay, you can evict him - hence the reason for the lease. Sounds harsh doesn't it? Would I do this to my son? Yes, if he was as out of control as yours, I would have already have put him out. But mine knows this, he knows his options once he graduates high school and none of them include being a rude slacker in my home.
What was the punishment the first time he got in a car accident? If nothing, then of course, he doesn't expect punishment now, and didn't think it was important to tell you about. And why are you paying his insurance? As soon as he started driving *your car* he should have been contributing to the insurance cost.
The problem is, your son's attitude and general behavior did not happen over night - so he doesn't see why he should have to change. He has been getting a free ride, with no consequences for ugliness, for a very long time. You have obviously been putting up with the disrespect and violence for some time now. You have a set a precedent that he can walk all over you. The only way to change that is to put a plan in place, present it to him, then stick to it. And that is the hard part - you have to be hard and fast with your decisions, no waffling involved - if you make a plan, then don't stick to it, he will continue to walk over you and cause dissension in your home. Your younger boys will then begin acting the same way to you when they see no consequences for behaving badly.
Don't let him, and don't let yourself, use the excuse that his father has not been in his life. My son's father is a severely poor father, and often absent, but my son does not treat me like dirt nor is he allowed to use the "no father" excuse to behave badly.
Make a decision regarding your son, and stick to it. It is not going to be easy, but he needs to grow up and take responsibility.