Not all dogs are meant to become mushers, or dog sled racers. If you have a dog over 35 pounds with good 'leg', they can be trained to pull, regardless of the breed.
If you are interested in learning about mushing there are many online sled dog organizations that can help you out. You can also contact your local sled dog organization.
Skijouring or kicksleds are good ways to get started. Skijouring is where a dog pulls you while you are on skis. A kicksled is a light, upright sled that can take 1-2 dogs. Both are rather inexpensive options for the novice
In skijouring 1-3 dogs are used. In sprint races, the smallest team is a 3 dog team -- but you can run 2 dogs in the 3 dog class. Other sprint classes are 4, 6, 8, 10, and unlimited number dog teams. Distance races vary between 6, 10, 12, 16 and unlimited.
In sprints, the race is usually 1 mile per dog in the team. Some sprint races are much longer, especially in Alaska. Mid-distance is somewhere between 25-250 miles and long distance is over 250 miles. This will vary from location to location.