how big should a crate be for home use relative to the size of dog? We aren't sure if we want to use one yet, but as our downstairs is open plan, it may become a neccesity before long if chewing gets out of hand. The breeder of our pup lent us one for the car until we get our own one, but this doesnt seem nearly big enough for home use, especially not for when the pup has grown to full size (pointer size).. any advice?

It depends on what you intend to use it for. Ideally your dog should be able to stand up straight, turn round comfortably and lie stretched out in it so for a pointer sized dog probably a very big one!