We have had our first litter of 9 (medium sized) puppies, all has gone well and the last few are going to their new homes next week. We are keeping one boy and are unsure about where he should sleep. They are currently all sleeping in a big whelping box, with Mum. But when all his littermates have gone, do we use the crate for the pup, keeping him separate from his mother at night, put them in side by side crates, or keep them in the whelping box, which could make training more tricky (and also allow him to continue his mission to chew all our kitchen cupboards!!!)? Any advice very welcome!

How old are the puppies? I would actually recommend beginning crate training now, in terms of putting the crate in the room and allowing him to investigate it, leaving him in the crate for a few minutes at a time, etc. All of the litters I've worked with get used to crates from a young age for this purpose. Crate training is such a useful tool and since he's already proved to be destructive, crating him at night would be your best bet. Don't see any reason to crate mum next to him unless you normally crate her at night. If the other dogs are allowed in the same room his crate is in, however, I would recommend covering the crate if they're loose and he's crated so that they don't bother him.

We attached a crate to the whelping box from around 4 weeks and this became the sleeping area for the pups.  This was changed for a larger crate as the pups grew and was never shut at all, they all loved the crate as they could see so much more of their surrounding and the general hustle and bustle of daily life.  When we just had our one girl left we moved the crate into the dog room and she slept in there with mum and our other dogs in the same room but with the puppy safely enclosed.

when we kept a boy from out litter i have a small crate (for bringing puppys home) that i set up within the whelping box with a nice bed and a toy to cuddle upto, left it open for a few days, then poped him in and closed the door for 5 mins to start with by the time he was 10 weeks (we actually had another puppy here with him) and we moved him to the bigger crate and took down the whelping box, he was more than happy to go in there and sleep and have to say he was the cleanest pup we have ever had