I prefer the box to have no base. Keep the bitch in the box for whelping, then she'll stay there with her new pups. Don't leave it any longer than that or further complications may occur. There are a number of situations which can necessitate a caesarian section, and you must follow your own vet's guidance at this time. In the normal course of events however, the puppies will be produced at intervals over a period of several hours.
Larger breeds tend to have bigger litters, and vice versa.
Assuming everything seems to go well, leave mum with puppies at all times, ensure that all pups get a go at sucking, and take mum and pups to the vet for a check up within the next 24 hours. Sucking soon after birth is very important, as this ensures that the pup receives colostrum, which is the first milk of the bitch, containing large amounts of disease preventing antibodies. For the first couple of weeks, mum will suckle the pups. Then supplementary feeding starts around 15-20 days of age. The bitch should be wormed during pregnancy and then start worming the pups from 3 weeks of age.