I'd recommend having a look at a good cat book about doing the introductions, It basically comes dow to being slow and patient, but it's well worth knowing the details. I don't feel qualified to pass the information on and get it right, but I found this to be a good book (and its only a tenner or so from Amazon): The Perfect Kitten.

Definitely, definitely speak to the breeder AND your vet about injections. The breeder will be able to tell yo any that have been given, and the vet will tell you what others need to be done. It's a good idea to take the kitten for a chegk-up with your vet within a couple of days of its arriving, and ideally before starting any introductions to other pets.

The best food to buy is the same food as the kitten has been eating already. If you want to change to different type of food, let the kitten settle in fully first, ideally for several weeks. Then, to change foods, mix the new and the old, starting with plenty old + a little new, and gradually increasing the proportion of new. This will help to avoid emotional as well as digestive upset.

Really, the kitten should come litter trained. If not, then the most important thing is to never punish any little accidents. If you witness any such incidents, then immediately place the kitten in the tray, if this can be done within a few seconds of the accident, then thats better. Other than this, place the kitten in tray after eating. That's about al I can say, and again, I'd strongly recommend the above book.

HTH