
Why don't you go for a pedigree kitten instead -it's just like with dogs, you know what you're getting temperament and size wise and will then buy from somebody responsible with health tested parents etc. :)
Geeting used to dogs -the one essential piece of info is that the kitten MUST have somewhere to escape to, so that he or she will never need to feel cornered. Baby and dog gates are great because kittens will just walk through the bars of them!
We've had several kittens (and adult rescues too) that weren't used to dogs but they've all got used to our lot no problem, it just takes a bit of time and the best thing is to not interefer -other than to make sure the dog knows the cat is not a toy of course. :) Never leave them unsupervised together etc. If you get a rescue mog, most rescues let the kittens go very very early as a) they need to home them ASAP and b) there is a great fallacy amongst rescues and even vets that kittens should be homed aged 8 weeks. The shouldn't, kittens should be 12 weeks old minimum before leaving their mothers, but a rescued mog WILL cope -just beware it will be very small compared to a GSD and may try to suckle anything furry. :D
Food, in my opinion (and many other breeders too) you can't beat Royal Canin (and you need kitten food up until at leats 6 months), but other good ones include Techni-cal, Hills, Iams. I would never feed dried alone as it often leads to problems long term, so always feed one meal of each for adults, dried and canned, for kittens 2 meals of canned and 2 meals of dried a day. Denes is very good as far as canned goes, but also HiLife, and on the cheaper end Felix. I'd never feed anything like Friskies or GoCat or Whiskas dried in any shape or shop's own or similar.
If you want to feed fish now and then, best thing is to feed coley or cod boiled -cats go absolutely mad for it.