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That depends on the airline and the destination. Check how far in advance you need to check in, add the journey and some margin for traffic, and then agree the departure time with the coach company.
Pass on the flight number; then the driver can follow the arrival. Agree beforehand how long he will wait and what happens in the event of a long delay.
Yes. A trip to a Dutch airport is perfectly normal for a Belgian coach company. Give the departure time of the flight, and the coach company will take the distance and the traffic into account.