You do, all loans in Canada require this by law. You can pay off at any time.
I think he meant the "financial" ability to pay it off at any time.
I don't think so, otherwise the statement makes no sense. Take a 0% loan for the longest possible term sounds like a no brainer to me. If you want you can pay it off but there is no need to unless you just want to rid yourself of the debt.
Borrowing to invest is great too but you'd better make damned sure that you can cover any margin calls you might receive.
Longer loans mean you're upside down longer. If you're upside down on the loan and your car gets totaled then there's your margin call.
There is still some risk in taking the "free" money. If you can handle the risk then, yeah, I'd agree the 0% is a no brainer.