Take your height in centimeters, multiply it by Avagadro's number, divide it by Frick's constant, add in your weight milligrams and divide that by the square of the radius of the earth in inches, and you will have your answer. Seriously, I think a 660 would be fine, perhaps a 680 to get the best interest rate.
Not too much... I've got mine 9 months after having my first secured card with Capital One... They sent me the offer...