Nature of the Rottweiler?
Wanted to know does this breed have an unpredictable nature?
Rottweilers are just like any other breed of dog, and their nature is determined by genetics and upbringing. A well-bred and properly raised Rottweiler isn't any more unpredictable than any other dog would be.
In fact, the natural inclination of a Rottie is to be calm and confident, to observe rather than 'jump in' and because of this they make very discriminating guard dogs - knowing when, or by whom, they or their family are being threatened. A Rottie who is a good representative of the breed won't bite without good provocation and will use his/her size to intimidate if necessary.
They are very loyal and loving and extremely intelligent and easy to train (with positive methods only!) and make great family dogs. However, it's important to understand the breed and to pick a healthy pup from healthy, stable parents and to raise it with love and discipline which isn't harsh.
You may want to read my Rottweiler Dogs, Rottweiler Temperament and Are Rottweilers Dangerous pages as I think you'll find the complete answers to all your questions there.