driving a mosfet irf640 correctly

83 nC means the FET will turn on in 83 NS if you have 1 amp of gate current or 830NS with .1 amps. So if you want a gate resistor use 10 or 12 ohms. You will still need a heat sink depending on the duty cycle as the power disapation is 1.8 watts at 11 amps.

OK, no one else has asked so I will…

What is the end application?
Are you running a fixed duty cycle or is this a PWM scenario?
If it’s PWM, the switching losses may be fixed, but you have to also consider how I²R losses could change over the duty cycle range for total MOSFET power dissipation.