Shots-Puppies need at least 4 sets of vaccinations and an adult set. Can't afford it? Don't bring puppy home. Consider an older dog-who will need yearly vaccinations.
Food-dogs and puppies need high quality pet food to live a long and healthy life.
Exercise-backyard time alone is NOT exercise. Dogs and puppies need sustained play-and they need YOU in that backyard to play with. Don't want to go outside-don't get a dog, or consider a smaller dog who can do well indoors.
If you are going to leave the dog alone for hours in the backyard, for whatever reason, please do not get a dog. It isn't fair to the dog.
Crate Training-I consider crate training essential to living with a dog. There are just going to be times when you want them in a quiet place. Waiting till then to shove them in a crate isn't going to be a happy time for you or the dog.
Leash Manners-another essential.
Car Manners-yes, essential.
Recall-you have to have a good recall-a dog that you can call to you is likely going to end up lost or dead.
All the other stuff, agility, obedience, etc, is fun and I recommend it-but if you can't do these minimal things, please reconsider owning a dog.
Do not use a dog or puppy to teach your children that life is disposable or worthless. If you do not have time to honor the life you are contemplating bringing into YOUR life, please reconsider owning a dog.