To further elaborate, u can use larger than 16gb but xbox will format the drice n recognize only 16gb max.

depends on where the console is from - the shop can usually send it back for you to claim for warranty. chances of the xbox breaking down is very low provided your place your console in area with good ventilation (this is very important; don't block the exhaust vents), also beware of knocking/dropping it while it's running.