Valkenburg and Aachen, especially from the south of the Netherlands. From the centre of the Netherlands, Düsseldorf, Oberhausen and Liège are roughly the same distance.
For a Saturday in December, ideally as early as September or October. On weekdays there is usually still room later on.
Yes, the driver waits at the coach park. On a long day the waiting time counts towards their working day; enter your departure and return times and BusOffer takes that into account.
Yes, with a people carrier or minibus too. Enter the number of people and you'll see which vehicles fit.
Fill in your place of departure, your destination and your group, and compare the coach companies with their prices.