Can you ask the breeder for food suggestions? If you can't, maybe join a breed specific forum to ask for food suggestions.
Labs can be prone to orthopedic problems, and you need to feed a kibble with the proper caloric & calcium amounts. You want to grow a large breed slow, and too many calories and too much calcium can cause unusual growth spurts.
I can't remember the calcium ratios you need to look for because I raised my large breeds on raw food.
Also, please do no spay/neuter until your pup's growth plates close. Early spay and neutering can create serious long term health problems (orthopedic, bone cancer, adrenal disease). Sex hormones close growth plates on a large breed somewhere between year 1-2. Most mastiff breeders will ask puppy owners not to spay/neuter before the age of two. Boxer breeders generally wait until 18 months of age.
Your vet will try to talk you out of it, but I'm telling you, do your research!
Health Issues Linked to Spaying and Neutering Dogs
Save Our Dogs » AVMA’s advisory boards oppose mandatory spay/neuter
Dr Becker states that veterinary schools do not teach alternative sterilization methods in the US, but this is changing. My vet told me that our local Veterinary University teaching school are teaching new students partial spays, leaving ovaries intact.
This is great news, but it will be years before this is mainstream.