The ideal age to buy any pup is above 2 months of age atleast. One must see both the parents and the pups with the mother. There are a lot of breeders and a lot of imported dogs in India, but an imported dog does not mean that it is of good quality, so always see both parents in person and not in pictures.
The microchip number can be checked with an instrument which some vets have.
The best option is to go to various dog shows organised by KCI and see the GSDs there and decide for yourself what you like and what you do not like.
Mr. Desai in Pune is a very good breeder and you can contact him for advise regarding this breed. His number will be available from KCI, so call them.
There are various first time dog buyers blogs on this website that you can read.