I’ve owned several Labs and used to show in conformation and obedience. I love the breed. I do think 6 weeks is too young to remove from the litter. Any chance the breeder will keep the litter together for at least another week?
The time to start puppy classes is about a week after the first vaccination so well before 12 weeks. The key is that the exposure is to other healthy vaccinated dogs in a controlled environment. You can find some good information at dogstardaily.com The information is broken down into what you need to know before you get your pup, first week home, first month home etc.
As for feeding, in addition to appropriate calcium levels I only feed foods that have passed feeding trials during the growth period. I raised my last two Labs on Pro Plan large breed puppy. In addition to HDMS list you can find food suggestions here /canine-nutrition/hip-dysplasia-dogs/#comment-510071572
and here:/canine-nutrition/hip-dysplasia-dogs/#comment-513500240
