Binomial distribution

The probability that a passenger books a flight and does not turn up is 0.05. For an aeroplane with 400 seats how many tickets can be sold so that only 1% of flights are over-booked?

Typical survey sample sizes are about 1000 people. Why is this?

When is an experiment described by the binomial distribution? Why do we need both the condition about independence and the one about constant probability?

Are these scenarios described by the binomial distribution?