
Hi,
Take your puppy to your vet for a check-up in the next day or two, and you will be told when to bring it back for it's first injections. As long as your garden is not used by strange dogs your pup should be perfectly safe out there for housetraining (and general training) purposes. Don't forget to carry it around wiht you when you go out so that it gets used to the "outside world" and won't be scared when it can go for walks on the lead.
Regarding food, carry on feeding it the same as the breeder recommended for the first week or so - you should have been given a diet sheet and a couple of days' supply of food to keep you going till you can buy more. It is important not to change a pup's diet suddenly as this can cause stomach upsets.