Not so sure on the puppy food. I know with Oscar he never ate puppy food because he is a giant breed and puppy food has way too much protien. But I would guess to swtich him at 6 months.
I don't think it would be a problem now just feeding him twice a day.
i free feed mine. they do fine doing it that way. i split a can of merricks between them every other day and also give them natural balance lamb as treats. i have them on chicken soup for the puppy lovers soul and i just fill the feeder and leave it down all the time. if you dont have a doggie door and fenced yard it would be better to feed twice a day and at the same times, then you know to take them out about a half hour after they eat. my pups are 7 and 9 months old. i will switch them to the adult formula when they are a year old.