We just got a GSD puppy, and our older dog is 9.
Feeding wise , we just fed them together, and there have been no problems, but Ella the older one, loves the puppy and lets her away with play biting, which led to a vet trip....
Toilet wise, I swear by crate training - no dog will mess in its bed, and you just need to keep a close eye on them when not crated - first sign of a floor sniff and they;re whisked out to 'pooh corner'
Also make sure as soon as its allowed out, that you take it to a big field and let it off its lead - it will be so scared it will stick to you like glue, and make life and recall so much easier in the future 