hello there i have a few questions i am a new owner to a 10 week old pup

max he is so amazing i love him so much i am just woundering a few things llike he is almost 3 pounds is that normal ? how much should he eat in a day,should i leave food out all the time or break it up through the day? he scratches his ears a lot , i got him fron a pet stoer is that bad he owner seemed very nice and i know people that have gotten pupps from there that are healthy, does all purbread pups hve the tattoo on there belly ? and the last one when taking max to the vet can you ask to give a physical thing to cheak every thing ?
thank you all so very much nad sorry about all the questions