I believe anything over a 740 FICO score get's you the lowest advertised rate when it comes to car loans (in todays credit market). Probably around 3% at the moment.
I don't know about the insurance...
Assuming you have to stay with the company for a certain amount of time before you don't have to pay back the bonus. If so, I would put the signing bonus in a money market account and don't spend it until that time has passed.
I would also build up a nice balance before you start spending "big".
No offense to anybody here, but I've seen too many people having to sell their car or tuning parts, because something came up and they can no longer do without the money they put in the car. Having to take a hit on the sale...
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