1. While the pup is large and doing fine, take it away from its mother, and that can change fast. Puppies should not be weaned at 4 weeks, and changing the puppy's diet, how much of which is milk from its dam, unknown is likely to cause issues.
2. Even if the puppy is large, it's bladder is small, and its developement is at 4 weeks. You should not be trying to house train such a youngster, and you really can't keep it crated for any amount of time.
3. Right now all its confidence is coming from its dam. Removing it from its dam at this point and shifting who it gets its confidence from, may remove the confidence boost a pup gets when it leaves its first home and sinks or swims. It should only be done if the bitch is dead. This is bad for the pup and the dam.
4. You will have to wait for it to grow up a bit before you can actually start training it.
5. The puppy is probably still under the dam's immunity, and so you will have to keep it at home until it is at the right age to start receiving innoculations. And then some.
Just a few, I would call this breeder and tell them you changed your mind and are not going to buy the puppy from them. They are not considering the welfare of the pup or the dam.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC