A.H.
The general rule of thumb is-when he's hungry, feed him!!
The most formula you should give him is 8oz at a time (his belly can't handle more than that) & at his age he might still need that every couple hours-some babies are starting to go 3-4 hours between feedings by now, but it sounds like your little man has quie the appetite! At his age he should be drinking around 32oz of formula a day.
I would try to space his meals out about every three hours (thats how my daughter was, and still is even as a toddler) and give him a 6oz bottle and 1/2 cup cereal at each meal & see if that keeps him fuller for longer.
As far as sleeping through the night, there isn't much you can do to "train" him just yet...he's still young enough to need to be fed on demand (which, I know, is frustrating, but just keep in mind it wont be much longer!) When he is closer to a year and still isnt sleeping at least 8 hours, you can begin to wean away his night feedings. The best thing you can do is to give him a bottle right before bed (but DONT put cereal in it; thats an old wives' tale & is super unhealthy). That might keep his tummy full for a little while. A warm bath and a short massage might also help. Now is a great time to develop a bedtime routine- a bath and/or massage, reading a book to him, lotioning him, singing to him with the lights low,rocking him, whatever you choose. Once you do it (and do the same thing every night, in the same order), he will start to know that following all these events, comes bedtime.
Now: the pooping! Pooping is one of things that varies from baby to baby. As long as he doesn't go four days with NO bowel movement & as long as he doesn't have 4 or more loose stools in one day, he's fine. You're probably right in assuming he's just getting used to solid food. Be happy he can go that aften--my poor baby girl has the HARDEST time pooping & she screams in pain every time she goes :( I'm sure changing that many smelly diapers gets old, though, lol!!
I'm no expert on any of these issues, but I'm ANAL about everything concerning my daughter (I'm a first time mom obsessed with being a first time mom!), so I'm constantly asking the other moms in my life about their experiences and I read ALOT of different books, magazines, websites, ect. to teach myself all about her emotional, mental, and physical development & that's how I came up with all my answers!