RE: What age?
I think my wife got most of the books we own on line; try Amazon, etc.
Although, you might try a local bookstore first so you can actually page thru the book and see how extensive the chapters are on breeding. Some of the books we have don't have more than a dozen sentences on breeding.
Sorry, didn't mean to infer that you would become a puppy mill, just wanted to make sure you knew there was a lot of testing to be done if your goal is to produce healthy, long-lived puppies. Part of the problem with puppy mills is that they often do little, if any, testing, so they may end up furthering a serious health problem in the breed. As an example, in my breed (Cavalier King Charles Spaniels) Miatrial Heart Valve disease is a problem that responsible breeders are testing for. Once a year all our dogs go to a board certified cardiologist and if they come up with a heart murmur, they are spayed/neutered.
Hope this helps somewhat. Wish I could help you more, but I just don't know about specific issues with bloodhounds. Good luck!
Bruce