> I have owned German Shepherds for many years, and have always wanted to become a breeder of them
I think it's well worth being very clear about your motives - what do you want to breed for?
If you disregard the back yard or pet breeders that are looking for money, the experience of raising puppies, or the desire to recreate their own pet then you'll probably find that the 'breeders' that remain are those that do it to get quality puppies that are unavailable elsewhere. By that I mean they have worked or shown their breed in some capacity for many years and have found a need to breed that involves the betterment of a line or has a great quality dog that can really contribute something to the breed.
I'm sure as an owner of many years standing you already know what you like but have you found a breeder yet? When you are looking for a breeder it would be a very good idea to choose someone with history and longevity. If you choose the right person, long before you identify a puppy, the breeder will be invaluable to you in years to come. They may be able to help you show/work/train your dog and will give objective advice about the strengths and weaknesses of your dog. They can assist you with the necessary health checks and will have experience in choosing a good stud dog. Ideally this will be someone you can build a long term relationship with particularly as you may be on a waiting list for a while. A good breeder is likely to keep pick bitch but you may be able to get a strong 2nd choice. (There is a current thread about a puppy with a breed fault where you can read views about choosing at 7 weeks or running on). If you find a really great breeder they are bound to have a few they can't decide about which is a good sign.
If you're serious about the possibility of breeding in future have a think about how you might explain this to the breeder. Your puppy is likely to come with endorsements (I'd question the choice of breeder if it doesn't) and you'll need the breeders permission to lift these when the time comes. If you've built a relationship with the breeder, stayed in touch, had all the necessary health checks with good results, and can show your dog has merit in it's chosen field; there is no reason why the endorsement shouldn't be lifted.
Don't aim for a stud dog. Choose the best bitch you can, and be prepared to wait for her if necessary. Don't get two together - the best of breeders wouldn't allow it anyway. Don't worry about kennels til much further down the line. Good luck :)
**I should add that I don't breed and this is my view, rather than advice given with experience. Although I do have experience of choosing a great breeder - mine was excellent and a very good blueprint for the way to do things!!