The average life span of a Dane is 10 years which is the same as Labs, goldens, GSD and many other breeds. A well bred well cared for Dane can and often does live into their teens.
As far as books go there really is only 1 book out there that is factual and has true, knowledgeable info on Danes and that is Living with Great Danes by Jill Swedlow. There are many other "Dane" books but most have a lot of misinformation. Ms Swedlow has over 40 years living in caring for Danes. She has over 40 years as owner, breeder, trainer, handler & AKC judge of Great Danes.
Danes don't have any more issues then any other breed/mix. Many Danes live long healthy lives..If you buy from a responsible breeder who health tests, breeds for longevity, temperament & breed standard you dramatically increase the odds of having a long lived healthy Dane.
And YES Danes are very well worth it.