I love big dogs too, and mastiff's are one of my favourite breeds.

I've worked in the vet industry for over 10 years now, and I guess I have some advice.... the biggest advice I have is puppy school and formal training for the first 8-12 months. Than informal training (at home) for life.... Great Danes & Bull Mastiffs are both stubborn dogs. What you don't want is to have an 80kg dog who is out of control and able to physically take over. I've seen it, and had to get great danes tranquilised with a dart gun in order to give a vaccination... its not nice for anyone. Having said that, Mastiffs are some of the most beautiful dogs, they are gentle giants.

Large breed dogs have issue with bones, all of them do. As well as GDV's or bloat. I would get pet insurance straight away. It can be very reasonable if it can be included in with your own health insurance or home & contents insurance. Also, diet. Start on a well balanced diet designed for large breed dogs. Diet is very important from birth for large breed dogs, and home made food doesn't have enough calcium and magnesium for them, unless you are grinding up the carcases for them to eat all the bones yourself. I would recommend a good brand of dog food for the first 8 months. Those are the most important for large breeds.

I hope that helps!!!