To start a routine pick the times of day that you want him to sleep. At 4 months my kids slept at 10AM At 2 PM and at 6 PM and then would fall asleep for the night at 10 PM wake up 1-2 times during the night to eat and sleep till around 7:30 AM. 3 daytime naps is normal according to my pediatrician at that age. I made sure I fed them right before those times and sat quietly with them around that time to get them to sleep.
With my daughter I fed her rice cereal at dinner time because it seemed like I could not get enough formula in her, I don't think it helped her sleep though but she was happier because she was full. Please dont mix it in his bottle that is dangerous and a choking hazard.
Make sure that you are giving him everything he might need to sleep soundly at night to possibly cut the 2-3 times per night of feedings back to 1-2 times which is totally normal at that age no matter how big they are they still get hungry. (My son at 10.5 months still wakes up some nights multiple times and other nights sleeps all night long depending on if he is growing or not feeling well.) Make sure that he is warm eneough, keep his room around 70 degrees, use a sound machine or a quiet fan pointed at the wall to give white noise and fans help with air circulation(helps prevent sids), and most importantly make sure that he is warm! My son sleeps in a onsie, footie fleece pj's, a fleece sleep sack and one light blanket tucked in tight around his torso and legs. Think about how many blankets you use on your bed and make sure he has that many layers, when he is comfortably warm but not overheated he will sleep longer.
Good luck and be patient, all night is a long time to be away from you.