You should feed a young pup 4 small meals a day increasing the amount in the bowl as he gets older. By the time he's one year old start reducing the feeding from 4 bowls to 3 then 2 and if you think he can do with just one feed a day reduce it to that. Remember not to let him get too heavy as it's not good for German Shepherds hips. If you are feeding dry dog food make sure he always has clean water for drinking as the dry dog food swells in there stomach and soaks up all the natural juices. Make sure he has been wormed so he gets the best out of the food. German Shepherd's shouldn't be walked too much when they're pups as this is bad for their hips also.
No, read the back of the dog food bag it should tell you how much to feed him because if you give him too much he will get the runs and if you feed a large breed puppy too much you will put strain on the joints and he will not grow properly.
As much as he will eat.
I have three month old Alsatian puppy so how should height he have