Hostile intent doesn't mean you have the right to lethal force in any state. It would allow you to attack him certainly, and probably threaten him with a gun, but not to shoot him without further provocation. Which doesn't mean you wouldn't get away with it with a conservative jury and a good lawyer, but the idea of excessive force exists pretty much everywhere.
Wrong. See Castle Doctrine. And for good reason too. If I come home and find someone in my house that shouldn't be there, I'm not going to wait for them to attack me in any form or fashion.
If I repaid half of the money, I am still paying for it. I should get at least a partial refund.
No, because you drove/used the car. There are few things that depreciate as quickly as cars, and when someone buys a new one, as soon as it's driven off the lot it loses value. A simple trade would result in a net loss for the debtor.
What really happens in the business is that the repossessed car/house/etc. is resold or auctioned, and if the amount of money it brings is greater than the amount owed (very unlikely), than the difference is given to the person who defaulted on the loan. More often, it brings less than the amount owed and the debtor can choose to settle it there or pursue other collection efforts such as wage garnishment.
"A car is just a big purse on wheels." -- Johanna Reynolds