You should be correct about the number pulses/second. I would run these pulses into an interrupt that does nothing but increment a pulse counter. Then I would use a timer of a few seconds duration, and each time it times out, go get the pulse count, calculate your wind speed, and reset the pulse count to 0 for the next pass. Don't try to combine the interrupt with the use of the delay() function. You could get your timer output by just reading the mills() function, and doing nothing until the right number of seconds has passed.