Please please please run the breeders by someone on here first! There are SO many bad breeders out there, even the ones that love their dogs aren't doing it right.
Anyway, to your question!
I have a 6.5 month old GSD puppy, and 3 already resident cats.
At first Dino just wanted to play chase, none of the cats were happy! They've never lived with dogs before lol! One of them I was especially worried about, my 5 year old rescue boy who was SO timid, he wouldn't come near anyone when we first got him. He still doesn't like the dog, and will swipe if he comes near, but he's happy to sit in the hall with the dog wandering around and won't run off anymore. Indy is also happy to walk past him/under his legs but if the dog sniffs him too much he will swipe.
Pablo and Dino have a fantastic relationship. They cuddle up together and wash each other. Pablo even rolled on his back under Dino's face and started playing with his whiskers lol!
Dogs can live with cats fine, just when you bring pup home keep him on a house line so you can stop him from chasing. Do some clicker training and work on impulse control from day 1! Reward him for leaving the cat alone, but make sure you do let them interact calmly. You want them to know how it is acceptable to interact.
Dino still sleeps in his crate at night, although any day now I will decide to leave it unlocked - just need to tidy up my room first haha! I have been leaving him unattended for a while though. Seems like forever

The little puppy stage goes so quickly!
If you do get a crate then get the 48" one and get a divider to make it smaller while pup is young. You can use the crate to help toilet train, as a dog's natural instinct is to not soil its bedding area. If it has just enough room to stand up, lie down, and turn around then it will help immensly. Any time you can't watch pup, put him in the crate, and it will keep accidents to a minimum.
I honestly don't know what I would have done without our crate, and Dino still loves his and goes in it of his own accord for a rest