I used Retriever Training for the Duck Hunter by Robert Milner. It goes step by step and always works for me. There are other great books too which will be helpful because sometimes it takes a different idea to train a dog.

But a lab should retrieve from the start, just do not do too much, sitting to get food is also easy to train. Making it heel at this point seems a bit early to me butI think it is something that is mandatory in dog training.

I think the key is to never give a command you are not in a position to enforce such as calling for a dog when they are not on a lead and can run away.

But this book and many others push that you keep the dog in the house because it makes for a tighter bond as well as in a sense allows you to train them every day.