Hi! Welcome to the site.
I'm sure some of our breeders will be along with suggestions, but I can share from a buyer's perspective that e.mail or phone calls work for initial contact.
When you're dealing with a serious breeder having nailed down what you A) want to do with the dog (competition such as bite sports or agility or obedience or protection or jogging companion) helps the breeder decide if their program fits your desires in a dog
B) go check out the different lines and dogs (got to Schutzhund trials, shows, competitions that have German Shepherds participating). Often you can speak with the breeders and handlers in person to learn what to look for and what to ask for.
Most successful, serious breeders ask for a deposit on a litter. Then upon picking the pup up you pay the balance.
My suggestion would be to start saving up now rather then trying to negotiate payments later, set aside a 'puppy fund' so that you have all the money needed before
you go pick up your pup. That will make the transaction cleaner and show you to be a serious and committed owner and will be a plus in your favor when dealing with good breeders.