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.
Every breed can be trained to learn almost every command. However, some breeds learn a lot faster than others - making them a lot easier to train. These highly intelligent breeds pick up a command after only about five or six repetitions, they more often respond on the first time you give the command, and they remember commands even if they are not practiced often. They also learn commands even when the trainer is inexperienced and makes mistakes. So if you do not have a lot of the time to spend dog training, or you are the impatient type who gets frustrated easily, choose a breed which has a high ease of training rating.
Other breeding bills lump small breeders in with large commercial breeders. Small breeders are in no any way able to meet some of the kennel requirements written for large commercial establishments because they typically keep their dogs in their home as pets.
Dogs can either serve as watchdogs or guard dogs or both. A watchdog s job is to bark and raise the alarm when a stranger enters your property. Their job is to warn you. Many small dog breeds make great watch dogs. Whereas a guard dog s job is to look intimidating and protect his family by keeping intruders out. Some breeds are great guard dogs but not great watchdogs. And vice versa. And a few breeds are both great guard dogs and great watchdogs.