Breed
You have been thinking about having a bullmastiff. I recommend that you read some breedbooks and check the webpage of the breed club, where you can find the standards etc. Before you choose your puppy, visit some breeders at their homes and go to the shows to see different types of bullmastiff.
Bullmastiff is a wise animal. It is easy to train a bullmastiff because of its enormous appetite. Basic training is very important with this breed. When you have a well trained bullmastiff you can do almost anything with your dog. Tracking, obedience, showing and even agility are possible hobbies with a bullmastiff.
Follow the guidance your breeder gives you about feeding and excercising your dog. Bullmastiff is a massive dog who grows fast. Moving your puppy freely in a forrest or other soft bases is best for the puppy. Feed your puppy with proper quality food. With big breed it is very important not to overfeed young dogs. Keeping your puppy fit and thin is the best guarantee to get a healthy adult dog.