Keep in mind that large dogs are more expensive to keep. They eat more food, which costs you more money. Tick and flea preventives cost more for large dogs, as do other mediations.
You do not have to have own a large house to own a large dog (although a tiny apartment is not going to be big enough for one of the giant breeds). If you can take him outside for a good hour of two of exercise every day... a large dog can live in a small house or apartment just fine.
Dogs with short coats require virtually no grooming, just a brush and wipe down every so often. Pet dogs with long coats require either regular clipping every eight weeks or so (where their coats are clipped short) or there long coats need to be brushed practically every day. Show dogs, or dogs with long coats, require daily brushing or else there coat will become matted and tangled. Not only can it hurt your dog if he has tangled and matted hair, but it will also become dirty and he will look shaggy and ugly if you do not regularly brush his coat.
Though groups like the American Kennel Club make very specific designations about breeds and breed hybrids, there continue to be new breeds and breed variants developed all the time, as well as "up and coming breeds" not officially recognized by kennel clubs and experts. (Many dogs not purchased directly from breeders are also mixed-breeds of some kind, or have less than purebred ancestry.)