It may still be a little too soon to force him onto puppy food may not offering anything else but if he is doing well and active in another 5-7 days you could do that. For now the best approach is to mix foods, I would start with mostly baby food and a small amount of canned puppy food and gradually change the balance of the course of a week until it is all canned puppy food. Then you could go through the same process changing from canned to dry puppy food if that is what you like him to eat.
The first thing to understand is that your puppy has probably never been alone before so his anxiety about that is expressed as barking. Usually that will improve noticeably in less than a week if you approach it correctly. Any time you go back to his area while he is barking you are encouraging that behavior. You have to ignore the barking and not go back until he has been quiet for at least 30 minutes or after he wakes up. Other steps you can take that may help is using a covered cage (it will still take several days to adapt), having the cage in an area where he does not see or hear you and using interactive chew toys such as Starmark Everlasting Treat, Kong Quest or Traxx, Nylabone Romp n Chomp or processed bones or antlers (Blue Buffalo). Having music or a ticking clock can also help. The most reliable solution is a second puppy but if that is not feasible try these other suggestions.